The roof pieces are cut from 0.040 inch sheet styrene. They are sized so that the overhang at the eves is about 1 scale foot.
Campbell Scale corrugated metal stock was also used to panel the roof. In this case though, I made use of the full 12 foot length of the stock and didn't cut the pieces down to 8 feet as I did with the wall siding - the width though is still 4 feet. It does seem weird: cutting up the stock into 4 foot pieces and them gluing them all down again on the substructure. The difference is that the individual pieces, when glued side-by-side, form slight ridges that help give the illusion of individual sheets - which should be enhanced when painted.