Ok, so every tartan kilt I've ever seen has the tartan angled horizontal/vertical.
Has there ever been one with it angled diagonally, like Argyll hose for example?
I assume you would have to order/weave the tartan in square units of measurement, and then cut off the corners so that it becomes a large rectangle, and then continue the standard kiltmaking procedure.

I personally think it would look astonishing, imagine the pleating possibilities!