All my reference came from screenshots of the crappy polygonal sprites wandering around in Nibelheim. I made my costume to be the same basic shape, but I spiced it up -just- slightly by adding a faintly contrasting sash and hood trim. The robe itself is a light-medium weight cotton twill, and the sash and hood trim were made from supersuede.
The entire thing is totally black and enveloping, and the robe spills onto the ground and drags to give the effect that you might wonder if there's really anything human in there. I also wear creepy make-up with this costume to make myself look totally sickly and drugged out.
I decided to give myself the number 9 because Final Fantasy IX is my favorite game in the series. Therefore, I sport my number with pride. XD
The robe is fully lined with the same material used for the outer layer. That said, this costume is HEAVY. It's got about 8-9 yards of fabric in it.
I was really anal in making and ironing it - there was lots of turning inside-out, making sure the edge seams were pressed to the inside where they wouldn't be seen, lining up the seams of the individual pieces to match right, etc.
I matched up the supersuede pattern on the sash halves to make it continuous, and the tassled-edging was sewn on by hand.
This costume was perfect to wear in January for Anime LA, because it kept me pleasantly warm.
And to date, I have only had ONE person recognize what this costume was on sight without having to ask questions.
Anime LA 2005 masquerade - Best Master Workmanship, w/Special Mention for Design & Construction