I am trying to turn a tin roofed workshop into a studio and can't decide the best way to insulate the ceiling. I live in Louisiana where the summer's are hot. I thought about foil-bubble-foil and foam, or foil backed fiberglass batting between the rafters. There is no decking between the rafters and metal roof and there is a ridge vent. I want an economical way to insulate and keep out radiant heat, but also want to save on utilities later on. Any advice will be greatly appreciated.