These aren't too expensive to buy but it would be so easy to make with extra cloth, which I have a ton of. You could make any size or dimension for a nice custom design.
Make a big rectangle of cloth for the back, grommets for hangers or tube for curtain rod. The backing cloth should be thick or doubled for stability.
For the pockets, sewing long strips of cloth with all finished edges. Fold back and forth to create the pockets and sew along the bottom edge and side/between each pocket. Straight stitch to attach and zigzag over top for stability.
Make a paper pattern first to confirm size for pockets and get the right size for the backing.