i have a homemade rail in my backyard, heres how u go about doing it
straight rails are easiest, you can either by tube rails, or flat sheet rail. I purchased two 15' tube rails and made a double barrel shotgun rail.
the biggest thing in making rails is your welding skills. Shitty welds lead to shitty rails. Practice on scrap metal before you weld good steel together (cause materials for rails arent cheap, even if its left over scrap). Its better to get the weld right the first time then to have to grind and cut it off
c rails, s rails, require a pipe bender. Unless someones father works in plumbing or construction, your going to have to pay someone to bend the rails for you. So that all adds to the cost
kinked rails are possibly to build at home. You would need a large amount of welding or heating and bending skills
unless your really serious about getting into a rail making business, stick with straight rails made at home. Anything else is just DAMN HARD. Good luck