This project is actually based on half of a firehouse play set I purchased at Wal Mart for $5.00. The building is a decent size and it came with a bunch of accessories; some are scaled well and some aren't (like the fire trucks.)
The play set was modified slightly. The ladder running up the front was removed, as were the window frames. A handle also had to be cut from the center of the building, as well as the hinge and snap that held the play set closed when not being used (it also doubled as a carrying case for the accessories.)
Foam core walls were cut out and notched to fit into the sides of the front half of the play set, and a foam core floor was also cut and installed. The rebar- type pieces coming out of the walls are the rails from model railroad train tracks.
Squares of card were cut out and glued into place to create the sidewalk around the building.
Various pieces were glued around and in the building to complete the ruined effect. Sprue rubble was also used. Sprue rubble is simply model sprues cut into bits and glued into piles to create a rubble effect.
The entire piece was sprayed black, and a heavy coat of textured paint was applied. The building was drybrushed dark grey up to a white, as was the sidewalk. The various bits of rubble and accessories were painted various colors.