you will end up spending more money than just buying a new one, or get a used one on ebay. I have stayed in a wall tent in 40 below zero before, but it had a wood floor, blanketed walls, and a small stove. it was very livable.
I made my own teepee with canvas, I got a good deal on it by buying an old green army tent just for that purpose. it worked out very well. otherwise, canvas is high-priced unless you buy it in bulk. There are a lot of subtle sewing details involved in wall tents and you should find them out before you start, not after.