You can buy A4 size storage boxes which will stack and usually have a place for a label. They are cheaper that bookcases and can be folded flat when not in use.
I have seen theses things in rooms and houses and even some stores they come in different sizes, colors, and even shapes. usually rectangle though. and sometimes even connected together in like rows with sides and are freestanding.. I think its called a shelf? and when they are connected it like called a bookcase..
You can find cheap wooden crates that you can stack and move as you wish.
At the minute, my school books are in a tub under my desk but it really sticks out and it's annoying! So do any of you have any ideas on how to store them? Thanks x