Wow, thanks for the help Ron! I appreciate you giving away your secrets. The more I look at the design of it, the more complex I realize some of this sewing and joinery is, the more I appreciate how much thought has gone into it.
I wanted to make one, mostly for fun, b/c I realize I won't save much money at all trying to make it myself, but I also hoped to make it just a little longer to accomodate my 6'2" height. However, it looks like the 60" width of the roll becomes the limiting factor, unless I want to do more seams, which of course adds some complexity and weight.