For smaller things, I made one with foam core 1/2" thick. I duct taped two pieces together and covered it with flannel. I can just lay the pieces or blocks on or pin them. For larger tops, I bought extra wide flannel and made hanger sleeves on two sides (across the width and length). A 1" X 2" piece of wood slides in the sleeve to support the flannel wall. Two cup hooks get screwed into the top of the wood. This I hang in front of the closet in my sewing room from loops of string hung on metal eyes screwed into the molding corners, across the door. When I'm not using it, I can easily take it down and stand it up in the corner. If I have to get into the closet while blocks are on the design wall = then I usually pin them on, otherwise they'd fall off, when the flannel gets moved. I've even taken it off the loops, accordion pleated it onto the floor to get in the closet's bifold doors and put it back up with nothing coming off. Just needs a bit of straigtening. If I'm arranging blocks for a queen size top, I can lay the flannel piece down on the living room floor and use it flat. If I had the space, I think I'd prefer the flannel to be on a solid pinable surface, but since I don't, this works for me.