I made the costume last year and I gotta tell ya, they were harden than they look. I basically made my own pattern using a part of workout pants I owned. The red material was a heavier fabric (I believe poplin or something along those lines?) with the yellow being a cheap broadcloth and the black lines are bias tape.
You can take a look at my cosplay
and I'd be happy to try and answer any questions to the best of my ability!