Except for that coat.

Now, I am fully aware that there is no pattern in the world for Maka's coat; clothes simply aren't usually made like that. Still, I would like to sew it myself to save the hassle of shelling out too much money to get it online. So I guess my question is, how do you all reccomend I go about starting on it? If you have any tricks, or tips or some patterns to reference and modify, they would all be greatly appreciated!