Jewel costume AKA the super spandex tube top
Take measurements around your bust, waist, hips, and from clavicle to mid-hip. Make sure you are wearing the same kind of undergarments you'll be wearing when you're in costume (especially a bra). Using these measurements, take two pieces of white spandex and sew a basic, curvy tube.
Remember to sew it with the stretch stitch and stretch knit needle. Leave the top and bottom unfinished, we'll get to that later.