first make the lining just as if you were making the pants only longer.
sew the lining to the bottom of the waistband, folding the lining so that there is no raw edge, top stitch it from the outside to make it neater.
shake the pants down so that the lining comes down to the bottom of the pants, fold the hem lining under so that there is no raw edge showing and top stitch the lining to the pants from the right side.
