Abstract: A roof is assembled conventionally from cladding supported by purlins or girders extending between end walls of the building. The cladding can be metal. By providing a single structural spanning member, the requirement for girders or purlins is avoided and construction work is simplified. The usefulness of the structural spanning member is measured by the unsupported span that can be erected when the member is formed from sheeting material of stock width, conventionally with steel 1 or 1.2 meters, of a given thickness and rigidity. This member achieves the desired solution by a novel configuration in which the whole width of sheeting is utilized to form a single member having a top chord spaced from a bottom chord by a strengthened web, wherein pairs of chords of adjacent members nest to provide a single pitch of the roof.