First define your desired architecture! (Think Design your addition or house)
Then do some reading and planning! (for instance you might want to have your upstairs bathroom above your downstairs bathroom to make the plumbing easier)
Consult an expert or hire an expert! (They have the experiences of numerous projects rolled out successfully that are often very, very, very similar to what you are doing)
If you want to learn by doing, calculated in the learning curve, because you will make mistakes and you will want to have a plan for fixing the mistakes so that the system is not compromised. (Consider what happens when that addition to the house or the house is not built to code)
Reading: Take a peak at this great TECHNET content!