There is also the Recreating History: Inverness Cape pattern that you could look at.
I bought the pattern and it has a discussion of the evolution of the overcoat from the tight fitting overcoats
through to our modern suits.

Seems like a fairly decent pattern to use. I've even found some decent wool coating to use, (2 types, a subtle dark grey glenn plaid for around $5.00 per yard and a black and grey herring bone pattern for around $9.00 per yard), when I can get around to actually making the capes.