I dropped by my mom’s house the other day and she was whipping up some fabric covered file boxes. She’s a whiz at frugal decorating. I tried to catch all the steps she was doing. Hopefully you can figure out what was going on in my pics.
My mother is notorious for not measuring or anything so forgive lack of measurements. Most cereal boxes should be the right size. Just slip an 8 x 11.5 piece of paper in the box and if it fits you’re good to go. She also cut the tops off without measuring. Just make sure they both match each other so they line up when you fit the one in the other.