I made mine from a 1" thick board that is 18"x36". It fits right on a 2'x4' conference table by my sewing machine table. You could make yours any size that is best for you. I covered mine with an old piece of blanket cut tocover whole surface and reach around to the back of the board so you can staple it securely. Then cover with heavy cotton canvas (this fabric helps anchor your fabric as you iron). you can draw grid lines on it with a Sharpie if you'd like.
It does get dirty-looking after a while, but you just put on new canvas. It has worked great for me. Hope this helps :)