Abstract: A roof is provided for a building wherein inverted channels are secured along the tops of side walls of the building, these channels having upright projections at spaced intervals thereon. Rafters of an inverted channel section each has its outer end portion set astraddle one of these projections and is pivotally secured thereto. The confronting inner ends of each two rafters extending from opposite walls are joined together at the peak of the roof. Similar rafters are secured to each slope of the end wall of the building. Prefabricated roof panels with an understructure having transverse inverted channels on the under face thereof are lowered onto the rafters with their inverted channels nesting over the rafters and these channels are then bolted to the rafters. Tie rods are arranged to relieve lateral stresses that would otherwise tend to urge the building side walls outwardly away from each other.