Do you mean flat [a few feet of unremarkable elevation change] or flat [zero grade change]?
It makes a big difference. If you have sufficient natural drainage, then you can build something low-key. If it is really DEAD flat, you will have to do a bunch of earthwork just to get the property to drain.
Shadow Creek did have a fair amount of tilt to the site ... it's all created but it wasn't flat to start with. I would say the TPC at Sawgrass is really the best design from a flat site, but maybe Mark would disqualify it because Mr. Dye managed to save the trees, which few others would have figured out how to do.
Very gentle, unremarkable sites include Garden City and Kingston Heath [one small hill].