Re: CW Flash Build
I've seen some pretty decent versions of Capt. America's mask (from the films) that were done from pepakura files. Maybe take that approach, use foam if possible, and once you have the outer shape attach a layer of fabric to the outer surface? Could give it a formed/sculpted leather look. Just a suggestion off the top of my head, there.
EDIT: Since the mask seems to be more of a cowl and attached to the rest of the costume, perhaps incorporate a similar approach to the use of a faceshell in a Spidey costume? Like, the "shell" for the Flash mask would still have the fabric covering it, but that fabric attaches loosely around the back of the head/neck area?