I found a poncho with a hood. I am thinking you would probably rather do a cape (or cloak) with a hood. Seems like that would be more like draping a blanket around your body. But for the life of me I can not find a cloak pattern. I just searched the net for 40 minutes (cuz I wouldn't mind doing one for myself lol) and I came up with bupkis.
Maybe the poncho will lead you in the right direction.
What about a bathrobe with a hood ?