John & Cynthia's Wedding
A houppelande is basically just a long wide dress with giant sleeves. Or with "bishop's" sleeves. Or whatever you like -- there are lots of variations.
Here is a basic layout of the easiest version. This is a very brief
description! Do not try this at home unless you sew regularly!
What you can do for the sleeve is about 2" from the center on each side, make a 1" pleat. Then set-in the sleeve to the armhole. You may wish to make a .5" pleat at the lower armhole break.
Once you do that, just finish up the seams. Note that you'll need to do some sort of collar.
Be sure to try this on a very small scale model before you cut your
fabric! Make a barbie doll dress for a friend's daughter or something,
to this pattern.