So the game team I'm is trying to teach me modular sets and puzzle piece designs for 3D models. One example is a road with two lanes and a separate piece for the sidewalks. HE taught me this method for making the road a 90 degree turn on turns and on the outside there would be extra edges to form a box. So when you texture it you paint a road on it and than grass or something else where the extra edges are. My problem is learning this is quite complex.

Does anybody have any suggestions for building modular sets so they are easy to put together and tile properly?

Do you mean something like this? Bram's Eulaers' pic btw.

That kind of helps and I know I'm supposed to apply those concepts but this is for a mobile game on iPhone and Droid it has to be as little tris as possible.