Plaster Cloth (This is what I used to actualy make the mask. They sell it in craft stores in rolls. It's like $11. It's this cloth-like stuff that has plaster on it and when you dip it in water you can lay it onto a mold shape and create a mask.
A Plastic Face Mask (Use this as your base shape for making the mask. They're like $2. Make sure it's plastic though so the plaster will come off when you're done)
Paint (Yellow and black acrylic paint alond with a clear glossy polyerthane to finish it when you're done. You may want to also use primer before you apply the colored paint to prep the surface)
Some Paper cone shape (I SHOULD have used a cut up piece of thin cardboard or something to make the nose shape. The way I did it was I wadded up a lot of plaster cloth. You should use a toilet paper roll cut into a cone shape or something, secure it to the plastic mask form, and form the nose around it.
So basically you start with the plastic mask form and start building up plaster cloth to make a mask. 3 layers is good, maybe more if you want more stability. I made my mask with no eye or nose holes (OOPS!) So you should take that into consideration. You can probably make the actual eyes eye holes and line them in black. You should have enough room to breathe if you make the nose right... or you could add some holes. When it's done attach some foam so it doesn't hurt to wear, and attach an elastic string or band.