I used some leftover packaging (extra thick corrugated cardboard) and duct-taped the pieces together to make one big rectangular-shaped board.
Once you have a board of the size you want you need to cover it with some sort of material that will help your quilt blocks stick to it without pins.
This part is optional. I used some heavy-duty velcro. The kind that holds up to 7kg of weight. This stuff is strong.