Since some of the sites I have come across show a version of braies that are pretty much boxer shorts, I took a pair of Edward's elastic waisted shorts and drew off a pattern from them. Epic fail. The rise wasn't long enough.
Then I took another look at some of the pages that I had been browsing for patterns and decided to work on the rectangular construction theory. The seams were pulling in a bad place from side to side. In addition to the pieces you see below I added in some triangular gussets to make sewing the rise panel to the legs easier. Okay, got the waist, hip, and rise length correct, but the width of the rise panel caused some issues.
|Photo from http://research.fibergeek.com/2011/06/21/quickdirty-braies/|
Because he said that the rise panel was pulling in at the seam and was uncomfortable I have another thing I am going to try. I am going to modify the thorsbjerg trouser pattern and mock it up to see what I get as it has a wider seat panel. Looking at some of the sites and books it appears that the bagging that occurs in extant images of the braies could also occur here. Once I get it mocked up and he tries them on I will post an update.