Using ideas here, I made 2 design walls in 2 days! LOL
The first was 4 sheets of foam core boards (the kind for school reports 18x24) $1 each at the Dollar store. Taped them together with duct tape and covered with a felt backed tablecloth. This one worked like a charm, but wasn't big enough for the project I am working on. I also only taped on one side so I could fold this out of the way.
The second is a HUGE piece of fleece that got tacked to the wall near the ceiling. It's 60+" wide and hangs to the floor. It hold the pieces better than the table cloth--96 blocks hung over night without a single lost soldier! I also like that I can take it down and move it as needed.