FWIW,
I got the roof done on the highboy last week. It was really not too difficult. I had a piece of 4/4 pine that was clear for the length I needed and 26" wide. I had to rip it to a more manageable width (I think about 12-13"), then I resawed thin pieces on my bandsaw. I cut them about 3/16" thick, then planed them on a bench hook with a 1/16" lip. I found that a thickness of 1/16" or so worked well. Then I wet one side down with a splash of water and let it sit for a few minutes. Depending upon the orientation of the growth rings, the piece started to curl pretty soon. Using the curl to my advantage, I nailed the pieces along the curved top with no issue. I used four pieces, I think, with seams laid down along front to back stretchers between the back board of the pediment and the secondary wood back of the piece. I put some glue down on the stretchers, then sanded them flush when everything was done and dry. I'm including a picture of the finished roof. Hope this is helpful to anybody hoping to do this in the future. Thanks again everybody for the advise.
Rob