A semicylindrical roofing member includes an arch-shaped carrying rib and one cylindrically curved plastic sheet that rests on the carrying rib. At least one non-extensible strap spans the plastic sheet and holds it to the carrying rib. This strap is releasably attached to the carrying rib by catches at its ends. A strip of soft flexible material is positioned between the strap and the plastic sheet on the carrying rib and is compressed by the strap. As a result, the strap is held in position on the sheet under tensile stress and thus secures the sheet to the rib.