This section is from the book "Plumbing Plan and Specifications", by J. J. Cosgrove. Also available from Amazon: Plumbing plans and Inspection.
Furnish and fit up on the roof of the building where shown on plan, one wooden house tank 10 feet in diameter by 8 feet 6 inches deep, made of 2-inch cypress, cedar or white pine. Cover the tank with a copper screen of fine mesh to exclude mosquitoes and with a dust-proof wooden cover. Provide a hinged manhole 2 feet square through the cover.
The tank shall rest on pine timbers spaced about 12 inches apart and running crosswise with the flooring of the tank. The entire weight of the tank shall be supported on two steel beams furnished by the plumbing contractor. These beams shall be, respectively: one 15-inch 42-pound standard I beam 18 feet long, and one 9-inch 21-pound standard I beam 9 feet long. The two beams shall be tied together with two §-inch tie rods, and shall rest on four bluestone or granite templets 6 inches by 12 inches by 24 inches, provided by the plumbing contractor. The house tank shall be provided with an overflow pipe 4 inches in diameter, and a 2i-inch emptying pipe discharging onto the roof; a pump pipe and expansion pipe shall empty into the tank, which shall be connected to a 3i-inch galvanized wrought pipe to supply the building.