A prefabricated multi-layer roofing panel is utilized in a roofing system for low-slope roofs. The prefabricated roofing panel includes: an insulation layer that may have a self-adhering means on its bottom major surface for securing the roofing panel to a roofing substrate; a cover board that overlies and is bonded to the insulation layer, and a waterproofing membrane that overlies and is bonded to the cover board. The waterproofing membrane may have waterproofing membrane overlaps for overlapping and being bonded to the waterproofing membranes of other roofing panels in the formation of a roofing system. Preferably, the insulation layer includes interlocking structure for interlocking the prefabricated multi-layer roofing panels together in the roofing system.