Oh, buildings are constantly being built from sometimes extremely large blocks of prefabricated components.   But my point was not really along those lines at all.   It was just ... “plan the ending, and everything else from the start to the end, before you start.”   There is an excellent chance that the OP is jumping to a conclusion that, to solve this problem, it is necessary to “build” a rather complicated program.   It may well prove to be the case that nothing needs to be “built” at all.   That “buy vs. build” and/or “build vs. borrow” decision should be confronted as soon as possible ... recognizing also that the answer could be “partial,” in which both the scope and the nature of “what must be built” will change drastically from its present notion, and the choice-of-language will be driven by that finding.   That’s all.

“Laziness is a virtue...”   “Actum ne agas.”