My first attempt, based on my own interpretation of how such a cloak ought to be made, was a failure. Off to the internet, which I should have consulted first. The wonderful instructions here did the trick and had me slapping my forehead at my ill-conceived original approach. The cloak is cut in a huge half-circle, with the front edges on the selvedge, and a circular hole cut out for the neck. The long pointy hood is constructed from four kite-shaped pieces.
During the sewing, I had to keep trying it on, as swirling about the room was so much fun. The amazing qualities of the bias are very much at work in this simple garment.