If the fabric is not enough to cut a waistband using the same jeans material, use grosgrain ribbon to make the waistband.

To determine the right waistband length, cut a piece of ribbon ,3 inches longer than your waist length. Wrap around the ribbon on your waist , secure it with a pin then sit down and mark the ribbon to where you feel comfortable when sitting. Use a marking pen to identify the critical points (center front and center back and the two side seams). It is good to have a seam at center back as it facilitates alteration next time.