if you have a twin top-say 63" x 72" you buy 4 yards of fabric for your backing- cut it in half---now you have 2 pieces 72" x 40" (or so) sew them together---now it's 72" X 80"...Quilt your quilt trim to size, bind--and you have some scraps to add to your stash...you do not have to add borders if you don't like the look- do some math & buy what you need to make your back fit. or you can always purchase wide backs- they are available from 90" wide up to 120" ...some people like scrappy pieced backs- some like them to look whole. if you piece like the first example when it is quilted it is pretty much impossible to tell it's not a whole piece.