This doll artist has a detailed photo tutorial on sculpting an OOAK Art Doll Head/Face With Sculpted Eyes that she has shared with us. We really like this tutorial because it details how to sculpt a face on a cured skull-shaped under-sculpt made from polymer clay.
To size your doll's head, decide on the height of your doll and divide it by either 7 1/2 or 8 (it is helpful to use a proportion chart). Then just follow the 4 part tutorial. You will find it here: