Tim, figure out what you want/need in a possibles bag and make a pattern. I use poster board(paper) for patterns.The back and flap will be one piece of leather and the front will be the basic shape and size of the finished bag(minus the stitching seam). Between the two will be a gusset or the sides and bottom of the bag. With soft leather you will stitch the bag inside out and reverse it when done. By doing this it will get the rigidness it needs to hold it's shape. If you want a pocket inside you can add an extra panel to the front piece or to the back. Any raw edges should be rolled and sewn or put in a running stitch to prevent the leather from stretching.
Another thing that is important when working with leather is the stretch factor. Leather stretches more and easier across the hide and stretches less from head to tail. Use the non-stretch direction across openings and edges like the front flap and pockets and cut straps from head to tail for minimal stretch.
Osage medallions make for a nice closure button (
) on the flap with a thong attached to the front seam to hold the flap down.
