The access doorway is very narrow, and it's a pain in the neck (and sides, leg, and some other parts) to get anything large through, because once you're through, you have to twist the thing or hit the roof pretty much immediately. It's also partly full of stuff - spare mattresses, boxes of seasonal decorations, and stuff in storage for a charity bring-and-buy stall we run at conventions.
The plan is, essentially, to take out the dividing wall entirely, or as much as possible, and extend the bedroom floor and ceiling down into that space. We can then put screens or a curtain or something across where the wall was, if need be, but mostly it'll be storage space. A skylight will let in some light, the mattresses can lie flat, and we might even get a small desk or the like in there as well. And it'll be a matter of walking in, crouching a bit at the far side, but no more struggling through the narrow access door - and it'll make the master bedroom about 30% bigger.
The upstairs floor is chipboard under the carpet, and I think we'll replicate that in the soon-t0-be-ex-attic space; we can put down something nicer over it later on. The ceiling will almost certainly be tongue-and-groove panelling, which we both like, and which worked well in the bathroom. I'll need to leave access to the water storage tanks, but that can be behind a door, or maybe even a hinged set of shelves - access there won't be needed often.
A light fitting, or maybe some wall-mounted lamps, a socket or four, and it'll be a very nice extra space.