Polyurethane sandwich panels getting really popular for roofing these days. They made with polyurethane foam layer in between two sheets, usually metal or something like that. This make them strong but still light, and really good to keep heat inside or outside. People using them alot for warehouses, factories, and even some homes now. GLOSTAR produce high quality ones that work perfect for all this kind of uses. They save energy because good stainless steel clean room doors insulation, and can handle different weathers, so thats why smart choise for roof.