Hi Kitaye,
I've made mine measured to fit what I wanted, and the artist in residence here at my gallery just made one this week, because he liked mine so much.
They require one 8 foot board 2"X12". The ones from the big-box stores are usually yellow pine and make them very difficult to carve. You might consider another wood, or even gluing up 2 1"X 12" boards in order to carve it. They look great when pierce work is done on them as well.
The following links will give you some ideas of options.
I do enjoy mine. The wood cost me $9.00 apiece at the time, and I think they'll outlive me.
http://tech.cls.utk.edu/wood/project...chairplans.jpg Medieval Woodworking: The Bog Chair Mark III bog chair seat design on Flickr - Photo Sharing!
Thor