The clay mould for my mask sculpted on top of a styrofoam head (I would suggest plastacine or something similar. I just used what I had on hand, but a plastacine would work best). Liquid latex was applied in layers, with some toilet paper in weaker areas to add strength. Once it was all dry, I used creme makeup to paint it with translucent powder it set it. I did cut a small slit at the eye so I could see.
I made the dress from a thrifted large men's white button-up, which I took in at the sides to fit me, and removed the pocket and a portion of the sleeve. I modified the nurse had from a store-bought one, and gave both the dress and hat a coffee dye bath for about four hours. The shoes were thrifted as well, and I distressed them with sandpaper and scissors. All of these were smudged up with makeup to make them look dirtier.
The mask was attached to a bald cap, and then the nurse hat was hotglued on as well to hide that seam. The bald cap was given a paint job to match once I had it on, and then I used watered down creme makeup to paint my neck, the exposed part of my chest, and my upper arms/legs with a grayish corpsey colour. I added veins in a dirty green colour with an angled brush, and set it all with powder. Add a twitchy, zombie walk for effect!
(The flash in these photos washed out the colours, unfortunately.) I hope you like it!
ADDENDUM: I have gotten a lot of questions about this tutorial, how to use latex, where to buy it, etc. There are all kinds of resources on the internet about how to use special effects makeup, all it takes is a little searching! If there's anything you don't know how to do or where to get it, just google it. I can promise you that searching for yourself will get you faster results than contacting me personally. I made this tutorial as an afterthought, hence why it is so thrown together. Here I've given you a basic, simple description for what I did for my costume. There are many other ways to achieve similar results. Take this more as a general outline and get inspired to get creative with your own costume! Good luck.
And since some people have asked; No, I will not make one and send it to you. This was just a Halloween costume I made for myself one year.