I used Simplicity's #2333 pattern, heavily modified (the collar was a nightmare...). The front part of the coat (with the double rows of buttons) is actually a separate vest, as I started work on this costume before the game was out and concept art was lacking. The costume is quite form-fitting as it is (I don't think the coat in a maritime environment like dishonored's would be too fitting, but then again it's a video game not a historical reference), so I am actually quite intrigued to see what a female version of the costume would look like.
The mask is a painfull story of pepakura, ABS plastic sheeting, epoxy putty and green stuff. No casting, all sculpture. my reference was the 3d model that was available on dishonored's website. There are many problems with that mask, namely that a human face cannot fit in it (hence the larger jaw in my version, so I wouldn't have to hang it 6 inches away from my eyes).