Try looking at commercial patterns for a cape with a volume similar to what you want. There are yardages on the back of the envelopes.
You're about what the American commercial pattern companies (Butterick, McCall, Simplicity) consider to be "standard height", so you shouldn't have to adjust the length much, if at all. They use a base height of 5'10" for men's patterns.
FF9 cosplay? Hit me up!
I now have a Tumblr
. Sometimes I use it.