I actually found a similar costume on your website from 2010 and tweaked it.  My girls wore it last year and again this year for their school party.  We started with wire from Home Depot and shaped the wings…we connected the middle sections with a wooden dowel and lots of electrical tape.  I then cut some stretchy, shiny black fabric from Jo-Anns into two shapes for the front/back of each wing and sewed them together.  I inserted a backboard inside and taped it to the wooden dowel, and it had the adjustable arm strapped inside (think backpack without the storage part).  Once the fabric was in place, i painted the design using glow in the dark fabric paint, which was great when it got dark.  They were a huge hit!