Missouri Star Quilt Co has a tutorial on making your own pressing board:
http://quiltingtutorials.com/all/iro...tricks-series/
I made one recently. It is a larger one (24 x 48 I think). I purchased 1/2 inch plywood, it already came cut in a size I wanted. Used a layer of Warm and Natural batting, a layer of insulbrite, and then covered with duck cloth. I used a staple gun on the back. Love it! If you do it the way they do in the Missouri Star Quilt Co tutorial, the cover isn't stapled on, it makes it easy to take it off and wash it.