The Bum Roll Most research indicates that this garment was worn over the farthingale rather than underneath but for this pattern it is worn underneath and is the first item put on after your own undergarments. Be sure to stuff the roll well - it should be VERY firm. Be sure to pay close attention and mark the pieces as you cut them out. It appears to be based on an original farthingale pattern from about 1589, but with simplifications. Originally, the casing for the hoops would have been made by sewing tucks into the skirt fabric.
Today sewing twill tape on to the fabric is the alternative.
When sewing the casing on, be sure to leave a few inches open at the ends to enable sliding the steel through and matching the ends. If the space is too short you may end up inadvertently bending the steel to get it to fit, this will end up as a kink. Getting up will be a challenge and regaining your pride will be even more difficult. To avoid this keep you bottom hoop at least 4-6 inches above the ground, the longer your feet the further off the ground. If your skirt seems to be collapsing below the bottom hoop add a box pleated ruffle to the bottom of the farthingale.