Abstract: A roofing slab with vent opening which is arranged in a central region thereof and is limited by a peripheral edge collar and over which a cover extends in hood-like manner. A hose connection pipe directed towards a bottom side of the roofing slab is coordinated with the opening. The edge collar projects beyond the bottom side of the roofing slab and extends into a dish, and the hose connecting pipe projects on the bottom of the dish.