I am building a living space underneith a 25'x10' deck. What are the options for waterproofing that deck? I have already sheeted the deck. I have looked at gaco products. I have also considered a torch down with a floating modular wood deck above that. Any others worth mentioning?

Rubber roof would be an option there. There has been a couple of times we rubbered a roof and decked over that. I would use nothing else simply because how Long a good rubber roof last as opposed to tar build up/ torch down/ or mineral roll.