I would worry about the structure first. If there is a lot of structural work needed, it very well could require dismantling the roof to do that work (especially if it's the roof trusses/beams that need work).
Not to be a downer, but I think you may be in for far more work than you're anticipating to bring this unit up to snuff. It sounds as though you may have to rebuild a large portion of the house part. I'd suggest not making any firm commitments (or buying a lot of materials, etc.) until you've done the necessary disassembly and inspections and so forth to determine the full scope of what you need to do.