Here is another way that I have made a stone foundation. First photo shows four assembled sides of a building and four foundation pieces cut from "multi-scale cut block stone wall" http://www.sceneryexpress.com/.../productinfo/FL4150/ from Scenery Express. Note that the foundation pieces, made from urethane, have three courses of stone. The top courses fit into the bottoms of the walls so that two courses remain visible after assembly. Other types of urethane stone wall material suitable for this type of foundation construction are available from Scenic Express.