We built a few props. One was a flat roof where we used 2x12 and plywood for the deck. A layer of tar paper and shingles. It was about 10x10. This gave firefighters the feel for cutting and making sure they dident cut rafters. We were also able to work on having a back-up man using our SOG's back slaps for starting and stoping cuts. The best method it to get a vacant house to work on but I know how rare that is.