I'm with James, and don't see the advantage of an alloy roof. Yes, it may be more resistant to puncture but I'm much prefer repairing fiberglass to aluminum. White fiberglass is great, it reflects heat and doesn't absorb it. Weight is a critical factor, if you have anything over 150 pounds on your roof, you really feel it. I personally like less than 135 pounds up there.
Think of a roof tent like you would a sleeping bag. Buy what you need and nothing more. This way it is a lifetime purchase, you are buying it fo fit you and tailored to the type of climate and terrain you visit. Your vehicle may change, but your needs generally don't.
