A simple bender is all that is required, I think Harbor Freight sells one. The grade of steel and the thickness will dictate if heat is required. I have to ask why you want to manufacture your own. Other than the shipping factor, you can usually get them pre-made fairly cheap. Unless it is a situation or a job that requires "custom", it is by far cheaper to buy than manaufacture.
To get a good price in steel, you need to buy in large quantities, and then there is the time involved.