I recently built a fairly tall (~6.5') bookcase designed to fit flush against a wall. When it's flush at the base, there's about a 3/4" gap between the wall and the backboard at the top. Checked and the floor under it seems to be a bit out of level - something I didn't plan for. (I am reasonably sure the base of the bookcase is square.) Shim it? Pull out the block plane and take just enough off the base to get the case level?