it doesnt have to be perfect, buy any thickness pvc, drill holes in it at about 12" or 18" intervals, lets say your pvc is 2" by 12 and you lay two of them side by side, then get 2 x 2by4's 12 feet long. Screw your pvc to the wood and make a few a frames to give the rail height and stability. thats it, use pythagoras to get the right height you want. anything shorter than 12" is stupid, if you have the speed, build a high rail.
but the hardest and most crucial part is the drop it.