"what we might expect, in terms of 1) Time to completion, 2) Cost to implement according to the mockup, 3) Monthly server/maintenance costs and 4) approximate team size required"This question was followed by this acknowledgement:
"it is hard to make the above estimations, given the lack of clarity on the architecture which will be employed, and given the nature of software development itself."This is an understatement. The statement is generally well written, but the word "hard" is weak. It's not hard. It's essentially impossible.
I. The Conundrum
Let's say you decide that the budget for "everything" is two point five kajillion dollars. Clearly, you don't want to just fork that money over to a roomful of developers and wait a year for something to happen.
An Agile approach is a sensible alternative. Instead of building everything, you build a first release that does something. Ideally, something that creates the most value for potential users.
What's that first release? Presently, you don't have a formal, testable specification. More work needs to be done to define a first release. Formal and testable are pretty high barriers.
More important than details is this: there's a nasty circularity issue. Until you build something, you don't know where the technical roadblocks are. Once you build something... well... you've built something. And you're going to be building something potentially releasable merely to get to the point of being able to write a budget.
There's no way to know the budget without having started to build something.
Once you start to build something, you did useful work in advance of having a budget.
One (false) claim floating around the software development world is that we can somehow do more research to resolve the unknowns before we start actually building software. This is simply false. As we do "research" we're doing high-level design: we're building software. You may resolve a few unknowns, but there will be more.
The only way to know all the details about platform and the application is to build the application using the platform. We don't know anything until we're done building something that resolves some unknowns.
Interestingly, the definition of "done" cannot possibly exist. We'll return to the farcical nature of "done", below.
Worse, there's no way to know the budget without knowing the people who will be doing the building.
II. The Productivity Issue
Until there's a relatively stable team, it's essentially impossible to know how quickly programmers can build anything. And even then, there can be unexpected, unforeseeable problems with the team.
Let me tediously pound this point home with an even more detailed analysis. The point is to make it very clear that the future is impossible to predict.
Let's say the first release is essentially a clone of an existing open source project.
This is simple. What's the budget to clone the existing open source project?
Choice 1. Find an unpaid intern. (This may no longer be legal, but it's still popular.) Have them clone the repository, rebrand it, and you have something running. How quickly can they do this? You don't know until we meet the intern and watch them work. After they've cloned the existing open source project you then know how long it will take them. Until you've seen them work, you know nothing about the time they'll require.
Choice 2. Find a kid still in school who knows the technology. Pay them sub-minimimum wage to clone the package and rebrand it. How much will you pay? You don't know until you meet the intern and watch them work. After they've cloned the existing open source project, you'll know how much it costs.
Choice 3. Make up a schedule based on what little is known. Put the "clone the existing open source project" out to bid on http://freelancer.com and hope that others make bids that fit with your expectations. This is fixed price so the budget is—in principle—known. In order to be sure you get something high quality and usable, you'll need to write a lot of test cases and very detailed specifications. Sadly, that pre-work is of imponderable complexity. When you get bids that are too big, you learn that your specifications weren't good enough; and you need to fix your specifications to narrow the scope of work. Now you're doing much of the work (spec writing and test case writing) in order to get a proposal that includes your budget. Note the circularity where you're doing some of the work to figure out the budget for the work you're doing.
Choice 4. Offer someone a share in the company to clone the existing open source project. Now you don't have a budget at all. You merely have a schedule. When will they be done? You're back to option 1, the unpaid intern, except now with better incentives to be quick. But you don't know how long they'll take until you've seen them do it once.
Choice 5. Offer someone an hourly rate plus a share in the company to clone the existing open source project. Now you're back to having a budget, and perhaps it has an upper bound. You can pay up to some amount, after that the share in the company is their incentive to get something done.
I beat this point to death because there actually is no answer. No matter what strategy you choose, you still can't predict developer productivity. It varies by a factor of at least 10 to 1. Some studies show it varying by 100 to 1.
The idea of forecasting development costs is shameful lie created by accountants. Really. The GAAP requires controls and budgets before spending money and we're supposed to compare plan and actual. This is all farcical in software world. Software development is like R&D: it's structured learning and encoding the learning into software.
III. The Done Issue
One of the Great Lies is that software has a defined "done" state. This only true for reductionist classroom exercises. Real software grows, often without bounds.
"Wait," you say, "I have a vision of what I want, that defines a boundary."
Today, that defines a boundary.
In six weeks, after two releases and some trouble support calls and requests for new features, your original vision is out the window, and you're off chasing the things your real users really are asking for.
Only in-house IT managers for large (dumb) companies stick to the original plan in spite of all the lessons learned along the way.
Then you get partnership offers. And you see new platforms and tools, and you get more user requests. The browser landscape changes. Tablets become faster. Other changes that are impossible to imagine will happen.
The vision will not be stable.
It won't even be finite. A good business model grows and adapts and expands.
IV. Strategy 1: Estimate
What can you do?
Clearly, you want some kind of budget for creating some kind of software.
Clearly, there's no way to provide a good answer.
You can, however, find a farcical answer.
Step 1: find a developer who's willing to make a sincere commitment to a cost and schedule.
Step 2: trust the sincerity of their commitment, even though it's is absolutely going to be wrong. The Great Lie is that we might only wrong by a factor of 2. In reality we can often be wrong by a factor of 10: the $100,000 job turned out to cost over a million. (See above, 10:1 productivity is just one of the unknowns.) The million dollar job was ill-advised and cancelled after the second release, but the users were happy, so it was successful in many ways. But it was cancelled.
A sincere estimate is just a random number. However, many managers find that the sincerity gives them comfort.
Since productivity is unknowable and "done" is unknowable, a detailed estimate and plan means you must now spend a lot of time writing "change orders" and reallocating the budget every time you learn something new.
I'll repeat that.
When you have an estimate, all you do with it is reallocate the estimated budget as you learn more about the customers, the development team and the product. All you do is reallocate; the idea that there's "plan" which is compared with "actual" is farcical because the plan changes constantly. So constantly as to be meaningless.
[Accountants will claim that this is analysis wrong because the future is somehow knowable. I can only stare dumbfounded at them. The future is knowable? Really? They'll say that a plan is a commitment and comparing actual to plan somehow makes sense. They'll give all kinds of weird analogies that don't apply to software. Software development is not a "production" task like brick laying or making pins from wire. If the future was knowable, the project ROI would be a fixed 150% or 300% or, well anything. Oh. Right. Somethings are unknowable. Like the future. Ahem.]
V. Strategy 2: Agile
The very best you can do—indeed, the only rational thing you can do—is to locate talent who are willing to work for an indefinite period of time.
A person or people you trust.
You establish a release cycle. Two or three weeks are typical sprint cycle times. two weeks works well for very new development. Three weeks is better for more established teams.
You identify the first three or so releases by writing those high-priority, high-value user stories as carefully as you can. Testable, finite user stories. Clear boundaries on acceptable vs. unacceptable behavior. Too few user stories makes it difficult to foresee the future. Too many user stories can be needless preliminary work since they're going to change anyway.
You do Scrum development with a two-week cycle. http://www.ambysoft.com/essays/agileLifecycle.html
"Useless," you say, "because there's no overall budget!"
Correct. There's no overall budget. You don't (and shouldn't) have a legally-binding definition of "done". Done means "business death." You have a vision for the first release. From that you'll make enough money to get to the second release. Which gets you to the third release. You're not done until you're out of ideas and no one wants your product anymore.
Done should always be defined as "planned release [X] is the last release." After that, it's donate the intellectual property into the public domain and move on to something profitable.
"Then logically," you say, "There can be a budget for the first release."
Except, as noted above, you don't know how productive the team is. So there's no useful budget for even the first release. Ideally, 1 sprint = 1 release. But. Until you know the team, and the user stories, and the platform, and the application, you can't assume that.
Which gets us to this:
The budget is only enough to get you through the next two-week sprint. A three-person team for two weeks is 240 hours. $50/hr. $12,000 per sprint. Perhaps with a larger team, it may be $20,000.
Each sprint must produce something releasable or everyone is fired. It's that crisp. The company is out of business—as currently organized—when the team can't create something releasable. Either the user stories aren't testable or the sprint planning is too ambitious. Or someone lacks the skills they were thought to have during the interview process. Or something is wrong with the team chemistry.
Sometimes, a sprint's work product is not deployed for marketing purposes. It's saved up into the next sprint so that the monthly release is far cooler than the bi-weekly release.
I'm aware that this is an unsatisfying answer. It's nice to hope that software development is a finite, linear process with just minor bumps in the road. Sadly, it's not. It's a completely out-of-control process that hurtles down the wave fronts making progress in a reasonably desirable direction in spite of currents, winds and weather. It's (by definition) a learning process. As knowledge is accumulated, it's encoded in the form of software. Once all the knowledge is available, the software happens to be done, also.
And this: http://slott-softwarearchitect.blogspot.com/2010/03/great-lies-design-vs-construction.html.
This, too: http://slott-softwarearchitect.blogspot.com/2009/11/on-risk-and-estimating-and-agile.html.
Okay, fine: http://slott-softwarearchitect.blogspot.com/2009/10/breaking-into-agile.html.