I've made several rawhide sheaths. Have you decided on the type of rawhide you want to use? I've seen some made from cow rawhide- even some where they basically unwrapped a rawhide chew for material. I like deer rawhide myself - much easier to work with.
I picked up some videos by John Cohea from the Chris Crawford website. Lots of good information there. They're basically veg tanned leather wrapped with deer rawhide and stitched with sinew or waxed thread. Decorate to taste.
Happy to share what I've learned.