You should never use nails when installing turf on hard surfaces. When the space is surrounded by walls, we can simply lay the artificial grass directly on the drainage layer and the weight will keep it down. If the space is not enclosed, you'll have to glue a frame to the surface and staple the artificial grass to the frame.  Glue applications often leave marks and stains on the surface. However, it will not damage the waterproofing. We use commercial adhesives that are proven. We always recommend opting for professional installers as rooftop applications require knowledge of the materials needed.