How many sheets of plywood would it take to roof a bldg 40x60 with 412 pitch?

If a 412 pitch means a one third pitch then 20% needs to be added on to the area to be covered. So, for a 40ft x 60ft building, the total area to be covered is 40x60 = 2400 sq ft. Adding 20% or 480 sq ft this comes to 2880 sq ft. Next work out the area of the plywood sheets. Lets say 10ft x 5ft or 50 sq ft. So the total number of sheets is total area needed divided by the area of the sheets. That works out to 2880/50 = 57.6 or 58 sheets. A useful table for working out the area of a roof for various pitches is at the web link below.