I once made the style where there are plastic loops on the back with ropes running through them from the top of the curtain and attached to a bar at the bottom.
When you pull the drawstring, the curtain draws up until it hits a row of loops, folds over on itself and keeps goin until it hits the next row, folding over on itself once again. You end with horizontal layers of curtain at the top, with the whole thing being as wide as the distance between the horizontol rows of loops.
Does any of that make sense?.