I used a Vietnamese
ao dai for my inner robe. It's smock-shaped, but more fitted, I like the mandarin collar and side closure, and it's slit up both sides to about the waist.
The sash is simply a 3"-4" wide band of the same material fastened to you rpreference in back.
There's no clear and easy pattern for the outer robe yet. Lisa Yankey once made one, going from the original costume in the LFL Archives, and gave me her blessing to try to turn it into a real pattern when she got subsumed by law school. I'm still fiddling with the right side of the front panel, and then I need to scale it for differently-sized people and clean up the instructions a little more. I'm hoping to have it ready to go out to anyone in need by the end of the year.
That said, you can modify existing cape patterns to approximate it with a bit of work. The back half is essentially just the back half of a demicircular cape. A circular cape is one that, when you lay it out, it rests flat with the lower hem making a full circle. A demicircular cape is broken into pieces such that the lower hem is half the length it would need to be to be full circular. This makes more bell-shaped pieces than pie-shaped, and is important for getting the right amount of drape.
The front half is trickier. The right front piece must be cut so the front edge hangs straight down from the neckline (allowing for a couple inches to be turned under). The left front piece is the panel that comes across, and is mostly rectangular, with a hard-to-describe "swoop" up to the left shoulder.
If you've gotten that far, two 1" pleats to both sides of centre on the front panel, and one 1" pleat a few inches in from each side seam on the back pieces will give it the right drape.
The edges should be turned under, with the lining about half an inch further in than the shell so it doesn't show. And the bottom should be hemmed about an inch to an inch and a half from the floor when you're wearing your costume boots. Velvet will stretch slightly as it settles, so you
may have to re-hem, but the idea is that the hem just brushes your toes.
--Jonah