using Pythagorean Theorom, that is: a^2 + b^2 = c^2, after converting 72 inches to 6 feet you have 36^2 + 6^2 = c^2. this becomes 1332 = c^2, so c = sqrt(1332). then you need 2 multiply the answer by 2 for two sides of the roof, and add 12 (6x2) for the extra 6 inches on each side and you get 84.99 I believe.