Every few years I go through and eliminate sub-par paintings. The ones that are left (quite a few) are stored in three storage cabinets from Ikea. The six drawers are large enough to hold a half-sheet. I have three of these cabinets right now with one holding only unused paper, boards and printed reference photos. Similar to expensive flat-files, these cabinets are stackable. So, when I fill these up I can get another one.