how good are you at visualizing a pattern for stuff like that? i make basic patterns just with paper and masking tape. 2 crescent shapes will achieve that and then finish it with some heat forming. you could check out how sewing patterns are made, they can be helpful sometimes.
If you want premade patterns I know Kamui cosplay has a bunch of basic shapes and armor patterns available on their
website.
is that a fire nation pauldron?