Base is 0.020 styrene, I used a "FOR SALE" sign. It was about 12x18 inches from Walmart, cost $2 or so. The foundation is glued to the base. It's made from plywood, covered with brick sheet. The styrene siding on the building extends 1/16" below the bottom of the plywood side walls. The length x width of the plywood building (the inside dimensions between the back of the opposite side styrene siding) are the same as the dimensions over the face of the brick sheet. So the inside of the siding keys to the outside of the brick, aligning the church and the bottom of the plywood side sits atop the plywood foundation.
I did this so I could work on the scene on the work bench....and the church is easily removable to work on it and to work on the area behind it once I start blending the scenery to complete the scene. The only other structures with any kind of location device are the coal loader where there is a piece of stripwood to maintain the distance from the track buried under the coal on the ground under to conveyor.....and the coal dealer (with the silo) which has pockets for the columns made out of strip styrene (visible in photos on page 13in the thread). All other buildings simply sit in place, some are secured with a dab of white glue if I recall.