Learning Esperanto on Lernu.net, I've found that suffix -ej- is for space for placing something.
There are examples from this site:
lerni → lernejo = school dormi → dormejo = bedroom eliri → elirejo = exit libro → librejo = book store
The first three are obvious. But the last is not. I think that a space for placing books is something like a book depository. "Library" is not exact: In a library we can get books. A book store, in my opinion, is the place where books are being sold. Placing books there is not the main purpose of this space.
So, why librejo is not as straightforward as other -ej-words?