If we're going to talk about construction as the metaphor, then it's done by the computer (e.g. compilation), and it's so cheap or trivial on many projects that developers will ask the computer to build the software hundreds or thousands a times a day (e.g. via test-driven development). In this metaphor, I think the developer would be more akin to a designer or architect, but where the building in question is at least partially novel. If it's not novel in product, people, process, etc., then the client could just go out and buy or use one that has already been produced. The developer wouldn't be necessary.