Under stair storage. Much better then just a cupboard.
Built-in Closet Desk/Nook... Would be cool if you have a spare closet, so you don't have to use an extra room for an office.
60 Unbelievable under stairs storage space solutions
desk under stairs - Google Search
make a library cabinet--shelves slide in, end in first. This is a good how-to; there are guides under the tabletop and casters on top of the individual bookshelves so that the bookshelves have to stay straight when they roll in.