A Plague Doctor was a physician specializing on tending to those who suffered from the bubonic plague.They were associated with death (where there's plague, there's the beak doctors and also death).
Because of this a Plague Doctor's costume is creepy - also with the added benefit of it's resemblance to both The Grim Reaper and Ravens.
Step 1: Pre-Construction
To figure out the mask dimensions I constructed a simple form from newspaper.
Then trimmed and shaped it to provide a snug fit to my head.