Hi mowerman - glad you enjoyed it. Yes I considered the method you mention, but decided against it for a couple of reasons - the clearance I have for the fabric to 'pull' inside was quite tight and I was concerned it might jam/tangle (as it turned out there is enough room!) and the other was in case the fabric was too 'flappy' in the wind and I could use the interior loops and elastic cords to tighten it to prevent it from keeping me awake! To be honest I'd probably do it the way you mention if I was doing it again!
Cost? Well the basic roof commercially supplied & fitted is between £6k and £8k depending on where you get it. Add the same again for supply and fitting cabinets and interior fittings, water tank and waste, plumbing, gas, sink etc and maybe £3k for fridge, lights, solar panels, controller, mains hookup, battery metering and split charge system etc so probably all in £20k or so, at the very least to get to the fully kitted stage. My total cost for ALL that is currently £3500. Included in that is payment to the ally welder for folding and welding the corners, and the tentmaker for the stitching of the sides.
The basic roof material alloy costs, and all fittings for it, stainless clips and hinge, roof rack bars, yacht hatch, fabric etc is about £1500. The rest is the fridge, solar set up, various metering and electrical system bits, plumbing mains hookup etc. payment to welder/tentmaker and all the small things like bolts and fastenings which all add up, also mastics and sealers can run pretty dear too.
It did eat a shedload of time as well though!
PS - was just watching the Toyota video on Youtube the other night - cool truck but I think this one is in a class of its own: