this may sound odd, but I'd get flannel, like pajama stuff. It's more affordable than wool suiting, and because of the look it would be pricey to do that much of it. Then I'd do a lot of distressing and a little dyeing to get that nifty battle worn look. Use any halloween cape pattern for the drape part in back, that isn't anything special. Then make a separate piece, a very large triangle, for the front drape bit. I'd probably start with a two yard long piece*, fold it in half then just cut a straight line from the selvedge edge to the fold line (ish, this is battle worn so truly straight lines aren't necessary). This drape wraps around the body like a shawl, with the tiny point ends tying together behind your back under the cape. If it's big enough, it'll gather just like the picture all on it's own.
* this size is sort of average bust, size ten-ish American woman size. if you are bigger than that, or really busty, you may need a bigger shawl.