I have ds3 and ds4 doing a modified Sonlight this year, which requires tons of books. I got the bright idea that if I bought the books used I would save a lot of money. And, since I was planning to buy the books used, I figured I'd make a list of all the books that all of the kids would need (apparently for the rest of their lives) and have been looking for the books.
This results in millions of books! I'm still trying to figure out a good way to organize the Sonlight books, the fun books and ds2's high school books (yes, I'm a planner - he's only in 9th and I've got most of the books I'm planning to use through the end of hs). I started by buying little round dots to put on the official Sonlight titles. Well, the dots are labeled permanent, but they aren't. So I had to put the dots on and then tape them. Then ds3 and ds4 got into an argument about who would get what color. Luckily neither wanted pink, because dd claimed that color.
Now I have pink (core 1 & 2), orange (core 3), red (core 4), blue (core 6), dark green (core 7), yellow (core 100) and bright green (core 5 - the result of another brilliant idea - combining core 5 with Trail Guide to World Geography). Correct, that is 7 boxes of books. I only need three of the boxes at the moment, where do I store the rest? I'm tempted to go down to Home Depot and but enough wood to make huge book shelves. Not that we don't have 20 or so bookshelves already. What I have ended up doing is going to Sam's and getting their left over boxes with the cut outs and standing up the books in them. It's working so far, but I would really like a tidier method.