I suggest you make it at least as large as any quilt you "think" you may make. Mine is 7 1/2' x 6' wide. Right now I am working on a quilt that is about about 6" wider and longer than that. It makes it a lot harder to work on. I just used two sheets of the rigid foam insulation from Home Depot. Cut one in half and added it to the side of one of the panels. I don't have a cover on mine because I use spray baste and do it it all on my design wall.