Find the size of the main cables and the cross-sectional dimensions of the rectangular concrete compression ring for a circular suspension roof covering an area of diameter 305.6 ft. supporting a combined dead and live load of 60 psf. Allowable tensile stress of cable steel is 65 ksi. Compressive strength of concrete is 4 ksi. Use a sag-to-span ratio of 0.2 for the cables and a width-to-depth ratio of ½ for the cross section of the compression ring. Solve the problem for three different cable spacing at the compression ring of about 8 ft., 12 ft., and 15ft.