This is what I started with. Dirty beams, full of happy insects. No insulation. Water damage. Ugly partitions that made no sense. Flat walls with arbitrarily placed doors, which visually are just the pits. Floors that look more or less okay, until you try to do anything with them. No plumbing and minimal electricity. It was dark up there.
This is what we did. We made the place watertight. We used ultrathin insulation so we could still see the beams. We killed the bugs and treated and cleaned the beams. We replaced the leaky skylights with new ones that are approved for use in historic houses, plus we added a few. We added a bathroom, a bedroom and a kitchenette, which means plumbing and a whole lot of electricity. We broke up the utter flatness of that wall by putting in a closet. So we have one less door and a somewhat separate area for the kitchenette. Oh, and the floor? They — not me, my knees would never forgive me — screwed down every plank at about three inches on center. They removed the planks that were still too far out of whack, replacing them with other boards. They poured a self-leveling compound over that, put a foam cushion over that and oak flooring over that. I guess it’s good that you can’t tell that it was in such bad shape. Since the photo below was taken I have added a floor lamp in the corner. The light is too bright to photograph well but that corner is now a great place to settle in with a book.