first off how much steel does you have, second 20 degrees is a perfect pitch for a kink, then how high do you want the last section, 1 to 1 1/2 feet should be good, then going back to geometry use the cos function to find out high to build it (i.e. 10(length of section)cos20(pitch)=3.42) so add 1 or 1.5 to that and you get 4.42 or 4.92 feet. if your to lazy or stupid to do this than you have no business making a rail. Or get some nerd to do it for you