dude, thats awesome, if my prom had been a masque i might have gone instead of going to a play at pcc that night.
anyway, ummmm what are you trying to do. a good base thats kinda cheap is ahh, plastered gause, and you can like...lay it on your face while its wet and then be very still till its dry then clean it up and cover it with tissue paper or something.
you can allso buy very basic masks at costume shops, we could swing buy one sometime when were working on your project it you want.
and then you can make them more fancy from there. i once made a mask (from a prebought base) that was a bunch of dry leaves that i then shelacked. kinda a green man kinda thing.
you can also made a positive form a plaster cast of your face from paper pulp, but its not QUITE as strong. but you can get pretty strong if egg cartons are involved.
i guess i could give more specific help if i knew what you were trying to make happen.