Yesterday hubby and I made the box seat from scraps of MDF. 9mm thick for each end, 6mm for front and back, 4mm for the top.
Length 26cm, depth 12cm, height 9cm. Scrap quad glued into each corner gives it strength and keeps it nicely squared.
It was glued and nailed with tiny brads, then left overnight.
Today I made the loose cover from a fat quarter of fabric. I simply laid the box on top of the fabric, trimmed it to size and cut a square out of each corner.
Corners were then pinned, tacked and fitted. Fortunately there were no adjustments to be made.
I turned the cover right side out, slipped it over the box, folded up the fabric so it was flush with the bottom of the box, then pinned and stitched the hem . . . finished!.