I know this is an old topic, but I thought I'd add a resource for future reference in case others come looking. This year I learned (and am still learning) how to make masks out of 7 to 8-oz. leather (and thinner leather too). My main source of information, at least to start, was this tutorial video by Andrea Masse-Tognetti of Merimask Designs: http://youtu.be/obE333UphPg It was immensely helpful for me, and allowed me to realize that I could do this. So I jumped in with both feet and haven't looked back since!
Anyway, I hope this is useful for someone.