I presently have a design board made with white foam panels that I ducktaped together and then taped beige felt over it. It measures about 5 X 5 only because I don't have a tall wall for it. Sewing room is in upstairs of our cape cod house and the tall walls aren't in convenient places for viewing. It's portable so I can take it downstairs when I sew in our dining room. I also have felt covered panels behind my large IKEA desk for small blocks, pictures, notes, etc. I use a felt back dollar store table cloth as a portable design board when I want to take blocks for Show and Tell at guild meetings or for suggestions from members of one of my small quilting groups.
Picked up a few good ideas here and plan to replace fragile white foam panels thay have begun to crack with the firmer pink insulation panels, add a layer of batting under the felt and put up some of those command holders on the upstairs hallway wall. I can attach a large felt backed table cloth to them when I need a larger design wall - only thing is that I'll have to stand way back in the bathroom to view it, LOL! May in Jersey