Not to mean this is a bad way---every opportunity to add software to the small Amiga library is a good one---but if this software you are planning will indeed revolutionise the building industry, you probably need to make sure it runs on other platforms too. Fifteen years ago you could persuade a controller to get you very specific hardware for your work, nowadays that's a near impossibility.
In any case, back to your problem. You indicate you do not have much programming experience. Since you are intentionally vague (no disrespect intended) about the idea you had, I cannot say whether the program would be complex or simple. Nevertheless, I can still advise you very strongly to not start coding in C or C++ just yet. You are eager, you have this fantastic idea, and now it's all a matter of hammering away at the keyboard for a while...
Wrong. First, you need to think. What is it exactly that you want to offer? What is it that the user needs to do? How does the user have to use your program? What type of user are you targetting? Is it all point-and-click, or is there a fair amount of hands-on experience required? And so forth. Let your mind wander, but do not try to create something which Does Everything You Ever Thought Of. Do not rule out that possibility either: in other words, prioritise the features you want to implement. Once you've got that all sorted out (and believe me, this is a very hard step, which will probably take weeks or months to complete) you can begin to wonder about the next phase, implementation.
First you'll want a proof of concept, so use a scripting or interpreted language which hides messy coding details. Try Python, Ruby, Java or any other, but avoid C and C++. If you are planning to use a GUI or graphics, look for a language which has libraries for this sort of thing. There is a good reason for staying away from C at this point: you want to test whether your idea works, not whether your program is bullet proof. You don't need to be distracted by pointer conversion or class instantiation issues at this point, too. It also doesn't really matter whether the code you produce is sloppy, you can fix that later. (Microsoft has been doing that for two decades now, and it earned them a truckload of cash ;-).)
If, and only if your proto-program is working, you can wonder about the next step, which is tidying up, and wondering whether you need a conversion to a compiled language for speed. But chances are that this isn't really necessary. So to end my little story: think first about what it is you want to achieve, and then go out and buy some books about Python, Ruby, Java and similar languages. You could even stick to VisualBasic on Windows, or Blitz on the Amiga. As long as the language is simple, it's cool.
