I found the McCall M7000 official looking pattern and took my daughter to pick out fabrics. And then they sat there for a long time because I really didn't want to make the dress, but a couple weeks before our first Halloween party I decided I should get started.
This isn't really a difficult pattern, but it is probably the hardest pattern that I have made. Especially because the sparkly, stretchy knit (?) that I used for the sleeves was really obnoxious to sew with.
I decided not to make the overlay because it seemed like it would get in the way when she wore the dress to school, but I otherwise followed the pattern. My daughter is 6 and a half so I made the 5-6 size even though her measurements were in the size 3-4 range. It is a little bit big, but I am glad I made the bigger size because I am never, ever making another one.
Even though it's not perfect and I am only buying Halloween costumes from now on, my daughter was very excited about the dress so I guess it was worth it.