Making your own, or you need plans for the upholestry shop? A good shop should be able to give you exactly what you want, if you know what you want. Full tonneau - windshile to rear, or half tonneau - back of seats to rear, or what? Agree what you want and put it in writing.
When I need a new one for the JPS, I'm going to be sure it fits more fully into the base of the windshield. Your body may differ.