This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
For a flagpole extending from 30 to 60 ft. above the roof, the following proportions give satisfactory results: The diameter at the roof should be made 1/50 the height above the roof, and the top diameter 1/2 the lower. To profile the pole, divide the height into quarters; make the diameter at the first quarter 15/16 of the lower diameter; at the second quarter. 7/8; and at the third quarter, 3/4. Thus, if a pole is 41 ft. 8 in. high above a roof, the lower diameter is 1/50 of 41 ft. 8 in., or 10 in.; that of the first quarter, 9 3/8 in.; the second, 8 3/4 in.; the third, 7 1/2 in.; and the top, 5 in.
Flagpoles may be made of spruce or pine; Oregon pine is preferable, and where the entire sap-wood is removed by cutting the pole out of the heart of a large trunk, a durable pole is obtained. The pole should be painted with at least four coats of white lead, and should be capped by a suitable finial, terminating in a gilded ball. Halyards should be at least 1/2 in. in diameter, and be of waterproofed, braided cotton, or Italian hemp.