It's a square that has 2 layers, 5x5 except hollow. The corners also have bookshelves but you can skip 2 out anywhere for a door and it doesn't affect levels. Don't put anything except air inbetween the bookshelves and the table though, including torches and pressure plates.
EDIT: Oh, and the 2 layers are at the same level as the table and one level above.
two blocks high. basically the enchanter has a maximum of 30 bookshelves, allowing a doorway.
To clarify, there are 32 spots which bookshelves will help your enchanting, but the max benefit is 30 shelves. This leaves 2 spaces for use as a door. You can fill them, it just won't increase the level any further.
Also note that you cannot have torches on the shelves, and nothing at all in the space around the enchanting table- no torches, pressure plates, etc.
EDIT: Oh, and the 2 layers are at the same level as the table and one level above.
two blocks high. basically the enchanter has a maximum of 30 bookshelves, allowing a doorway.
To clarify, there are 32 spots which bookshelves will help your enchanting, but the max benefit is 30 shelves. This leaves 2 spaces for use as a door. You can fill them, it just won't increase the level any further.
Also note that you cannot have torches on the shelves, and nothing at all in the space around the enchanting table- no torches, pressure plates, etc.