A couple of thoughts. Modular design, so you can store it and move it. The biggest difference between model railroad terrain and gaming terrain is access, by that I mean the ability to place miniature so they will stand up (i.e. the ability to get your hand in and out of places). Model railroader are not worrying about moving anything about so they can (and do) go heavy on the details. During the course of a game session the characters can travel a good distance, trying to create terrain for every location just isn't feasible. Now, lets say you build a set piece for the climatic scene you can go into much greater detail and give it more of a flourish (if you will).

Don't get me wrong, I am not trying to dissuade from building terrain. When I read, "I'm going to make a whole map of it..." my first thought was that you intended to do an entire island...and then I am like naw...he didn't mean that...did he? :-)