My daughter was given one a while back, and my son has been asking for one ever since.
I finally found a kit on sale.
The instructions said to cut a 5 inch square out of each corner and cut 1 inch wide strips 5 inches long all the way around. I did 4 inches instead.
I tied a few on each side of all first to make sure it stayed lined up and tied the rest while covering up with it.