Aaron Foster from DCFD sent in these photos of three different roof props they have at the DCFD training facility. The first is flat roof, the second is a 6/12 pitch, and the third is a 12/12 pitch. The frames of the props are made with doubled up 2×10′s. The joists are made with 2×6′s (with 2×4′s on top) attached to the 2×10 frame with joist hangers. The 2×4′s are on top as sacrificial pieces that can be easily (and cheaply) replaced after someone runs the saw too deep. The props are mounted to telephone poles that are buried into the ground. The cut surfaces are simply sheets of plywood that can quickly and easily be removed and replaced after each training exercise. The painted areas of the prop show the “do not cut” areas, and ladder placement on the pitched roofs. These props are an extremely simple and effective way to teach (and perfect) saw technique. It allows for a large group of people to observe the cutting operation to maximize on the learning opportunity.
The photo below shows the entire frame without the sheeting, you can see that the sacrificial 2x4s are not yet in place.
The picture below was taken with the prop upside down on the bay floor. Its just a closeup of how the 2×6 fits in the joist hanger with the 2×4 on top (actually on bottom in this case since the prop is upside down)