This is not a step-by-step, because the steps I took to get a mask out of the materials are quite clearly steps that only I could have taken. The door plates are also pretty unlikely for anybody else to have. This is to say, it was a personal journey, and making an instructable for a personal journey would be like making an instructable for a sneeze.
But personal journeys are very often inspiring, if not directly instructional. So here are some photos of it happening. And maybe after you see them, you'll want to make your own mask out of what you have or find. Super good!
The only advice I can give you is: if it looks like you could make a mask out of it, play with it! Also don't drill through thick metal with a Dremel, you'll spend twenty minutes on each little screw hole. Use a full drill, although Dremels are super cool and have many cool bits that will eventually go through.
The diamond shaped plates: They used to cover the inner workings of a doorknob on our door, as you can see. We took the door off and used the old doorknob on the new door. The plates were left behind and I looked at it and thought, cor, I can do something with those. I played with them and stuck em on my face till I had an idea of how it would work. I think they're brass-plated steel but that's me talking out my bum. they feel good and smell like pennies.
the strap: I went to the thrift store with my lovely girlfriend and got her to go nab a belt while I grabbed:
the padding: a small length of blanket material. so warm on your face. the "scraps" corner of your thrift store's fabric section is an inspiring place. a couple of dollars expended. cut the straps longer than you'll need.
the bolts: as you can see we have a fantastic screwbox. family heirloom. If you don't have one ask a friend or start collecting. I picked a couple really nice simple wide ones. this ain't steampunk but it's close, and every visible piece should contribute to the look you want. Remember you deserve to have a really good looking final mask, and it's easier than you think to get the right bit. Make it happen! otherwise you'll notice the wrong bit every time you show it to somebody else. this is true of art in general.
the tools: use what you got and what you can get. it's worth hunting for the right tool, too. I always thought builders and artists were fussy till I started building and arting. the right tool makes the entire job something you don't have to strain to do.
the process (not shown): drilled holes through the plates, cut the belt a little longer than needed, poked holes in the belt, bolted the straps to the plates. Cut the blanket material in a single mask-shaped piece, hot-glued it to the plates, so that it connected them together in the middle flexibly. Voila!
the rest of the pictures: That's me and my brothers and our various girlfriends (on respective laps, thank you for asking. not always respectful laps, though. a ha) I'm on your left. My older brother is the one I was building the mask for, because he's going to Montreal. My younger brother is interestingly enough a very skilful plaster-mask maker. He doesn't do a lot of other art besides cooking and sassing, but he can mask like he's born to it.
the model: my brother, modelling the mask. I originally wasn't sure whether to make it in fox-orientation or sadface-orientation. I was pleased to see that it was flippable and both could work
the occupation: Go out and visit your local Occupy! You may not have the time to set up a camp, and you may not be sure if you agree with all of them, but what the heck. think of it more as a gathering than a well-formulated action. Some of the consensus building techniques (if they're being used well) may blow your mind. You may meet a pretty girl! This is my Danish cousin and a friend.
Good luck and good learning!