Purchase a Lycra bodysuit and a pair of tights for your costume. These items are usually inexpensive, and they are extremely difficult to make unless you are an accomplished seamstress.
Purchase at least 4 yards of sheer fabric. You may need more fabric to make a large or extremely long tutu.
Cut the fabric into 6-inch strips twice as long as you want the finished tutu. For instance, if you want a 12-inch long tutu, cut the fabric into 24-inch-by-6-inch strips. Cut at least 20 of these strips and up to 40 for a full tutu.
Measure your waist and add 25 inches to this measurement. Cut a length of 1-inch-wide ribbon using this measurement. If you have a 30-inch waist then cut a 55-inch length of ribbon.
Lay the ribbon flat on your work surface. Fold one piece of fabric over the ribbon and line up the ends of the tulle. Tie the fabric strip in a knot where it overlaps the ribbon. The knot should be tight enough to hold the fabric strip to the ribbon but loose enough that you can slide the strip of fabric back and forth along the length of the ribbon.
Continue to tie the fabric strips to the ribbon to fill out your tutu.
Wrap the ribbon around your waist and push the fabric strips to distribute them around your body and form the tutu. Tie the ends of the ribbon together in a bow to hold the tutu in place.