How much cloth to order for skinning?

I know I am way early in my build, but I want to make sure I order enough canvas/duck/cloth to cover my trailer (if I find a sale).
Anyway, it is shaping up to be a 5x10 TD closer to the Grumman 2 profile. My feeble calculations are looking to buy 7+ yards of 57+" wide cloth for the sides and 5 yards of 67+" cloth for the roof. Wide and long enough for shrinkage, I hope.
I don't mind having extra, but also hate wasting cash.
Other suggestions are welcome.
All answers will be helpful, and smart-aleck ones get extra points towards the grand prize.
Alan
Anyway, it is shaping up to be a 5x10 TD closer to the Grumman 2 profile. My feeble calculations are looking to buy 7+ yards of 57+" wide cloth for the sides and 5 yards of 67+" cloth for the roof. Wide and long enough for shrinkage, I hope.
I don't mind having extra, but also hate wasting cash.
Other suggestions are welcome.
All answers will be helpful, and smart-aleck ones get extra points towards the grand prize.
Alan