One way to make the backing is to make it out of scraps too. I made a quilt and wasn't in the position to go out and purchase backing fabric for it, so I just used up the leftover fabric, augmented with a few new FQ's. It turned out so cool! I used a simple design for the back and those I've shown it to have raved about how nice it is to have a reversible quilt. I felt so clever after hearing the compliments, when all I was trying to was save money yet still make an attractive back for the quilt.