I used this for my Steampunk Plague Doctor cosplay for Supanova 2012 in sunny Brisbane. There were no tutorials, so I had to make one myself and I'm quite happy with the way it turned out. I'm terribly sorry if I'm bad at explaining though - a lot of this was trail and error and hopefully if it's not 100% helpful, it will at least give you ideas on how to make your own :)
Gather your materials. I used:
1. A metre of faux leather.
2. Plastic craft mask (One that fits your face)
3. Masking/electric/easy peel-off tape (for the pattern).
4. Press studs and whatever for decoration.
So take your plastic mask; we're going to use this to draft out a pattern. The reason we're using a mask instead of a face is because it's much easier to operate over this than use your own face.
I drew a black circle around the mouth a nose to mark out where the base of the beak is.
Now, divide the face in half and cover it with masking tape. This will make our pattern.
Now, I used a hair clip stuck to my mask to estimate how long the beak is.
Now, continue covering half of the face with masking tape. Make it as layered as you like in order to make it sturdy when we peel it off.
This is what it should look something like this covered in the masking tape.
However, I do suggest adding to the surface space of the top side of the beak, it'll make it more bird-like and easier to sew to the underside of the beak.
On the inside, it looks something like this. The masking tape has made the pattern, or shape of the plague doctor mask.
While it is on the mask, mark out the parts of the pattern. Then cut it out - you should get parts like this.
I sliced it on the temple and beak base because these are the parts of your face with curvatures. Without these seam lines the mask will be too flat and oval-like. It makes it seem a little more comfortable and realistic if it can sit nicely on a face anyway.
Now, trace that pattern onto your faux leather and cut it out with about half-inch of allowance. Faux leather is nice because it's cheaper, more flexible and thinner than real leather.
Then, when you have the pattern, pin it together. This part will be trail and error, so once you do pin it together, hold it against your face to see if it sits right and isn't puckering. It might be uneven on both sides, but when you fiddle with it enough it will sit right eventually.
This is how it looks flipped ride-side up. You can fix the eyes later.
This is how it looks pinned up together (and stuffed so you can see the shape). So, basically, you can see how it's going to sit.
Also faux leather is quite sturdy, so you didn't have to stuff or bone the beak to keep it up. As long as it's symmetrical and sewn up, it will stay up like a crow beak.
Sew that baby up.
Try it on again!
This is the mask undecorated without a strap, but I decided to wear my cyberpunk goggles with it.. for some reason.
Now add your steampunk decore. I put strips of faux leather over the seam-lines to make it a little more leather-worked. Then used press-studs that look like rivets over them. I gentle brushed them with black to make it look rusted.
Afterwards, I took plastic sheeting for the eye lenses. I then put red cellophane under the plastic to make the eyes red (not pictured).
After that, add a head strap. This can be so different depending on your own design. I just used some more faux leather straps and an old mini belt-buckle clip.
Then wear it with your Steampunk costume with it... yeah... this is a bad shot, but I couldn't find a nicer one.