I started the outer gown by making a top from the Butterick 6134 pattern. I made some Changes though in that I made it a bit bigger, and shorter. That allowed me to pull the top over my head so I didn't have to worry abut zippers or other fastenings. The top was made from applegreen poly chiffon interlined with a nude poly lining.
The fit wasn't important since it was supposed to be a very loose gown anyway. I can really recommend this pattern, since it has raglan sleeves it so eas to put together. The original calls for it being unlined, but I have preferred to put a lining into it both of the times that I've made the pattern.
After that it was simply a question of pinning the remaining chiffon fabric and sew it on at the bust. I pleated it rather than gathered it since I think pleats looks so much nicer and gives a better drape as well.
My handstitching weren't quite up to scratch though and now when I've unpacked the gown I can see that some of it has come undone, so I will need to fix that before I wear it the next time.
It really is a costume that's hard to pose in, since it looks so much better when it's moving. I loved to just twirl around in it.