Overwatch designs can be a little tricky if you are doing it on the fly. But thankfully Blizzard has released the reference guide for each of the characters. Use it for your waifu Mei cosplay or for creating Rule 32 Hanzo art.
Personally, I think I could probably use these to pull a really steampunk D.Va poster off. Or merge the universe of Warhammer with Tracer into making something more blood thirsty. Those are just a few ideas that popped up looking at the guides.
If you are looking for a specific character, you will find this table of contents useful, otherwise take your time looking through each one -- remember to share with your art savvy friends.
If you used these reference designs for your art, make sure to link it back too so we can check it out.