Here is a project you can do to use up your empty cardboard boxes. I used Huggies diaper boxes, but you can use any kind as long as they are all the same size.
The shelf is actually sturdier than I expected it to be, but if you are going to use it for heavy books, you should use boxes that are the same height as the majority of the books so that the books help support the shelf and keep it from sagging.
To make this shelf, I first cut the flaps off the boxes and glued the handles flush with the sides. Then I taped the boxes together with packing tape. Once the boxes were joined together, I used Mod Podge to glue fabric squares all over the boxes. I didn’t cover all of the inside of the shelf because that part will be covered up when I put my books on them.
So now I have a cute little bookshelf, and I didn’t have to spend a cent for it. Well, unless you count the glue and tape. And it looks even better with the books on it.