The first thing I'd do is make a pattern out of some heavy paper. Take your time and get it right because paper is cheap and leather is expensive. Trace around the paper pattern on your leather and cut out the shape you want. If you need to form the leather a little bit to get it to take a particular shape or curve throw it in some water and let it soak for a minute or so dependingon the thickness. Set the peice aside for a little bit and let the water permeate through the thickness of the leather and evaporate off of the surface, then form the leather to whatever shape you want it to take and let it dry that way. When it is dry, oil it. Plain old vegetable oil or olive oil will probably be the easiest to get and will work just fine. Put enough on it to make it soft, but don't saturate it through and through with the oil. If the leather is saddle skirting type leather it may not get soft enough to suit you and you might be better off looking around for a scrap of chap leather to use as it will start soft and stay soft.
