When both daughters were still home, they fixed up their room with shelves all along one wall. They were allowed to buy huge concrete blocks with 2 holes. Then they padded them and covered them with heavy knitted old bedspread material and sewed it tightly to fit. Then they covered old boards they sanded down (under parental pressure) with matching or contrasting fabrics and thin padding. THEN they took old cardboard boxes and cut them to fit the bookcases, taped and glued them together and covered THEM with matching fabrics to store things in. They also made lids to fit. This kept them from arguing for weeks as they worked together!!!!
I've more or less added some like that to my shelves to store this and that.
Now if I'd only remembered to label them~