To answer some questions: chasw98: I will be using a wide blade seal around the sides of the sliding room to keep the elements out and the A/C in. Thus the gap between the inner roof and the framing for the outer roof will be as narrow as possible. I would love to have skylights but most RV skylights are domed on top and would not cooperate with the blade seals. Also, I just had an afterthought: The trap door for the opening will actually rest on the roof of the slide room when in use. A skylight would also interfere with the operation of the door. Here you can see how close the tolerances will be, if you can imagine all the exterior layers installed. I have decided not to wire the bedroom for electrical or sound just to keep things simple. This is my first build so I wanted to do things as simply and frugally as possible. Not just to prove that it can be done, but that it can be done on a thin dime. zjrog: What type of steel would you use for the studs? I would love to have used steel but in my mind the size, shape, and thickness required for any real structural integrity would just be too heavy. BigBaron: Diagonal braces are a good idea. Had weight not been a constant concern I most likely would have done a good number of things differently with the framing. I have an alternative plan that has seemed to work great so far. Once the framework is complete the voids in between the studs are filled with precisely measured and cut pieces of styrofoam, exactly the same thickness as the 2x studs. I'm jumping ahead a little with this photo... These panels are cut to fit and pushed in by hand. In addition to this the interior and exterior paneling is nailed and stapled respectively every inch or so directly onto the studs. As a final assembly it will have far more structural integrity than any one of its components alone.