Abstract: A plant carrier (9) for coated flat roofs lies on a buoyancy body (7) which extends over the whole plant carrier (9) and carries this independently of a water level on the flat roof always at a spacing from the water surface (h1). The buoyancy body can be slab-shaped and perforated by vertical bores, or consist of a granular material. The dammed-up water can be used as use water.