I just completed my Queen Serenity costume and a finished the Princess Serenity costume that I made for my roommate.
The Queen Serenity was actually rather easy. There is a great Vogue patten that is basically her dress. I made her rather last minute as one of our group had to back out of the con. The wig is the first wig we got for the roomie's Princess Serenity, but it was too small for her head and not the greatest quality, but it was available for this last minute cosplay.
Princess Serenity was a much more complicated beast. That is about 3 dress patterns Frankenstiened together and all of them vastly altered due to the fact that no one makes plus sized patterns that anyone actually wants to wear. I did all of the work on the bodice by hand including hand beading the pearls on for her circles. I even styled the wig from an Arda Chibi and a long ponytail clip.
Care to take a look? http://www.cosplay.com/photo/3219644/