http://vector.tutsplus.com/tutorials/illustration/how-to-create-a-3d-floorplan-in-illustrator/

"In this tutorial I'll show you the process I use for creating a 3D floorplan from scratch, in 6 easy steps. This technique can be applied to infographics, such as escape-plans or to show the layout of a building that you normally wouldn't be able to see. Let's get started!"