It is cheeper to buy them new, check out eztbucket here in the vendor section, but if you have the tube and can thread it, sure why not build them, look at speedway, or any other company, easy to copy from the pictures, speedway even has the measurments on their picture page, you will need to build the front batwings and rear mounts also.
I've seen people build them out of water pipe, but IMO that is just suicide. The correct way is to use seamless tubing. I just buy mine already done because it is one more thing out of the way and they work.