I have always felt that the 10 psf dead load for roofs is low. Some of the higher end composition roofs can run 400 pounds per square (4 psf). When you add plywood (1.5 psf), insulation (0.5 psf), 5/8" gyp board (2.8 psf), mech & elect (0.5 psf), misc. (1.5 psf), trusses/girder trusses or 2x12...