I found that the hardest part of making a cable is keeping the length relationship between the inner and outer pieces the same as the original. In other words, you don't want the inner too long, or it will not work as expected, too short and you'll never get the travel you need. Figure out how much longer the inner needs to be and keep that relationship. You can extend the working length of the cable by extending both the inner and the outer by the same amount. Different ends I made myself depending if it's for the clutch, the throttle or a brake. I used silver braze or "silver solder" to hold them in place, I never got standard solder to ever work for soldering the ends on as they just pull off.
Silver solder requires an oxy-acetylene torch and proper flux.