I have long wanted to do something like that and finally got the BMW E65 donor. Long studied similar homemade in the internet and finally started).
It must be said that the BMW body is doing very well, I needed a couple of hours to gently separate the trunk from the rest of the body.
Separated the trunk.
As much as possible, extra details.
Then, from the profile pipe, the frame was welded for the sofa.
From plywood did sidewalls, back and seat.
Polyester resin with fiberglass.
Street details for upholstery. The upholstery did a wonderful master Pasha. Made everything neatly and efficiently!
The first fitting - everything came out without fittings! Next Paint, assembly and here is the result!