Firstly, the idea to do this came from terribly overpriced roof racks.
After a couple of hours of looking at what Lowes had to offer I chose these.
50 ft of 3/4 inch schedule 40 sprinkler pipe, 20-3/4 "T" connectors, 8-3/4 pipe to 1/2 threaded connectors, 8 special adapters called "Universal" for disassembly, and the corners are 3/4 90 degree angle with the 1/2 threaded offset X 8, to give the roof rackyour choice of height.
Total cost 45.00.
Step 1: Measure as you go
I built this roof rack one measurement at a time. Keep in mind that as you measure, depending on where you want to put fittings for support you will have to count the inside measurement of each fitting otherwise it will be short.