The shirt was really easy. I bought a tight maternity shirt and a doll from the thrift store that had hard arms/hands that I could detach from the soft part of the body. I painted my arms grey to get that zombie look.
I ironed on some patches to the inside of the shirt for extra strength and then cut holes, smaller that the arms and then push through.
I poured some fake blood (you can make it yourself with food coloring and corn syrup) over the edges of the arms and then quickly held the shirt up and left it on a hanger so the blood ran downwards.
For the zombie face I used craft glue in some spots by itself and some parts with one layer of tissue stuck to it. Once the tissue is on there you can make holes, scars, cuts etc but using your fingers or a tool. The parts that are just glue, let them dry slightly, then run your finger beck over them so there's kind of a hole in the middle, it looks like rotting flesh.
Once everything is dry - around 30 mins or so you can apply make up. I just used eye shadows (black, grey, purple, maroon and green) to get the dead skin look and then black under the eyes, around the edges of the face and along the lines in my face. The purple, maroon and green work well over the fake scars to give the look of bruised, rotting flesh. The middle of the sores I used black food coloring on a Q-tip to show depth, then the final touch was red food coloring on a Q-tip for the blood on the sores, and fake blood for inside the mouth, tears and nose bleed. I just colored my hands with the grey eye-shadow, using the black to contour around the bones. I used black food dye for my finger tips which I regretted later because it does NOT come out from under your nails LOL
I think it turned out pretty well since I had no clue what I was doing. Apparently I was so scary that our neighbor's kid wouldn't come to the door ;)