project bonus room: built-in shelves with a slanted ceiling. dsc_0180. built in alcove ! ikea billy bookshelf hack bookcase modified to look like built in alcove. vintage leather armchairs trimmed with nailhead give this space a clubby english look. i wanted the bookcases to look built in, however i made the false wall in the library 1/2\” deep , but the bookshelves are 1\” deep. see more of the billy built-in with a top. built-in-bookcases-on-opening-of-living-room-.