Abstract: A system for roofing a substructure has a plurality of roof panels, a plurality of support members and a plurality of cap members. The roof panels each have a horizontal channel section bounded on a pair of opposing side edges by side flanges, with an upper end of each side flange bent to provide a groove opening outwardly laterally from the panel. The support members each have a pair of oppositely extending base flanges and a pair of oppositely extending top flanges, the base flanges and top flanges being positioned along a vertical web member. The top flanges are adapted to be received in the groove of one of a pair of adjacent roof panels and one of the base flanges of each support member is adapted to fasten the support member to the substructure. The cap members have side walls to retain the top flanges in the grooves without fastening the roof panel to the support member, thereby allowing some relative movement upon deflection of the roof panel.