Over my many years of making mistakes I've developed a few rules and tips. I guess it won't be too big a mistake to share them. So here goes. I've never seen a big project that gets done on time or within budget. Many never get done, period.
Big projects seem to take on a life of their own.
They grow and grow, and by the time all of the feasibility studies and planning gets done, conditions have changed so much that the final product, if there even is one, is no longer applicable to the situation that exists at that moment. I never accept big projects. When someone comes to me with a big project I break it down into as many little projects as I can. Any part of the project that can stand on its own is treated as a separate project. I always try to make mistakes that will become obvious quickly.