I dont' understand the roof-mounted tents. I see them a lot on ttora (toyata forum). They are very $$$ and unless you are hiding from lions, a regular tent is easier, quicker, and lets you spend money on more important things like gears, axels, lockers, tires, etc.
From what I have heard, with practice you can have some of these open and set up in less then 5 min. Thats from when you park, NOT when you dig the tent bag out of the truck. Unlatch, flip open, climb in.