Find fabric that is breathable and tightly woven. Make sure you have enough fabric, so you can have several layers. Get two hair bands. Create your super-cute mask! Make sure mask fits snuggly and you can breathe easily. You could probably use a pipe cleaner to shape the mask over your nose. You should wash your mask every day. Let me see what you create!
(Disclaimer: Obviously, these masks are not as protective as medical masks...but this will help in a pinch)