I would suggest you use masonite sheets, cut to any shape you desire, screwed down at the corners and/or toward the middle of each outer long edge to prevent warping. Glue eveything to the masonite, and you will have no loss whatsoever. If you don't want to glue the buildings down (for inserting lighting, later, for example,) that's fine, too.
Here is a wide variety of examples of how I use the method I just explanied...
