This is really simple. All you do if find a loose fitting dress, and pin the whole dress onto your fabric, and cut it out. No need to even make a pattern. Then, make sure the neckline is what you want it to be, I just did the same scoop in the front and back. Then, you sew the sides together, leaving room for the arm holes. And don't forget the top of the straps! Finally, you take scraps from the fabric you just used and fold the edges of them into the dress. I cleverly sewed them on while heming the neck line! ;D Put it on, slap on the ribbon, and you're good to go! :)
Please let me know if these instructions arent clear enough!!!