Larry,
You will need leather for the slide, let's say 8-9 oz, and leather for the loops, under 7 oz. The leather for the loops will have to be cut to width, any ornamantation (?) done to it, dyed (?), edges finished. There are different ways to proceed, if you want the rim of the carterage to ride on a shelf, you will have the loops sewn onto another piece of leather which is sewn to the looped slide, or the rims are stopped by the loop. The loops are sized for the cartdrige and sewn in place, do not groove on the loop side, as the leather is thin, and the strength is a plus. Then fold the piece in half, (welt or no welt) and sew. You would probably be well to give yourself an extra 1.5 inches extra on each end, after cutting to center the loops after them all, then edging. Don't be discouraged if you have one or two practice pieces.
Marc