If you need a visual; take your top to the fabric store. Lay the top onto the fabric you have chosen. Add 4-6 inches extra to the top and bottom. Have them cut two pieces at this length. Now, all you have to do is go home and sew the sides (after the selvedge is removed) together. Yes, you are going to have scraps (mighty fine scraps I will add). OR, you can buy fabric that is 108" wide and cut it at 60". You will still have scraps, but you won't have to make a seam. Hope this helps!