My roommates and I decided to make our costumes last year from scratch. We purchased fabric and “Buttercup” made the dresses using her sewing machine (of course she had the other two Powerpuff girls help a little bit with their own as well). We kind of winged it by laying the fabric, folded in half, on top of a dress we already had to get an approximate size. We then cut the fabric, but left the top (the fold was where the neck is) together. We sewed the sides together, but left the arm holes open. We then cut out a neck and the dress was done! We used the extra fabric for hair pieces and bought black fabric to tie as a belt.
A lot of people loved it even if they had no idea who the Powerpuff girls were. We got compliments all night. We wish we could wear the dresses again this year, but the fabric stretched out as the night when on. We could have purchased a more durable fabric, but we were in love with the shine and sparkle of the fabric we found. It also made the costumes more like our own personalities and gave us more satisfaction than buying a store-bought dress.