Making the "hood" of my head

So I have (for the most part) finished with my Yurei other than furring, but I'm not sure how to sew the hood (neck, back of the head) seeing as how I don't have a cast head or anything to have a basic form to make a pattern for the hood. Any suggestions?
This is my progress so far (except it is marked with sharpie) https://www.furaffinity.net/view/15309392/