HI again, I've just recently had my DH build me a big board that fits on top of my ironing board. I did a search beforehand & found this webshots site with clear step-by-step photos. I just used the 22" x 59" top measurement from the original big board. I have really enjoyed it, and wonder that it took me so long to decide to try it.
http://community.webshots.com/album/180862212jmSjuv