Hi. I am trying to find out how long to cut the 2x4's on my new chicken house roof.I am cutting the ends at 45 degree angles. The house is 6' tall. It is 4' wide and 8' long. The part I am trying to find the measurment for is black and has red lines. The brown is just the frame. Any help is greatly appreciated. Any formulas anything. Thanks a whole bunch. Dusty