I fold my fabric in half .selvege to selvege, then I fold it half again (fold to selveges). THEN I wrap it around my 6x24 ruler. By doing the second fold before wrapping it around the ruler, you keep the end from having a big bulge.
I have one closet that is pretty deep and for these shelves I fold the fabric selvege to selvege and then wrap it around the 6x24 ruler and store it flat. I reserve this closet for lengths of more than 3 yards.