I have made a dust ruffle before and what I did was go to the thrift store and bought a fitted sheet the same size as the bed. I put it on the box springs and marked with a marker where I wanted to sew the ruffle on so that it would "hang" right and then sewed the ruffle on the line I marked. I am not a fan of using just a flat piece because it always seemed to me it moved around everytime I changed the sheets. With a fitted sheet it doesn't move at all. You just have to make sure that the old sheet you use is the same depth as your box springs.