In Suruga Monkey Part 2 of Bakemonogatari, Kanbaru's room is literally full of red hardcover books. Why is this and what does it represent?
That's her massive collection of BL (boys' love) books (which she is also into, besides considering herself a lesbian), at least that's what they represent. As many other things in Monogatari's animation, it should be taken more symbolically than literally. Take for example Senjougahara's "arsenal" of stationery in episode 1 of Bakemonogatari, or even more obviously the constantly shifting, multiplying, growing, falling etc. pile of pencils in episode 6 of Nisemonogatari (you'll know when you get there :) ).
I believe the books (which are from BL) can represent the mental state of the character, who is also homosexual. Maybe that's why it's all a mess, and when Araragi goes to Suruga's house during a long conversation, they arrange (literally and metaphorically) her books (feelings). Perhaps this is why, in the Nisemonogatari tidying scene, when Suruga gets confused in the conversation, the books fall into a domino effect, and when Araragi helps Suruga to find herself again, the books arrange themselves. But that's just my interpretation