my thought is
I would ignore the 45 degree corner and just build straight out from the angle. You could have a hidden compartment behind the cabinet.
It's just a weird shape, so I'm wanting to simplify it by going straight across.
Then let your imagination be your guide, drawers, seating, overhead shelves with doors etc. Add some fluted trim and details to make it look like the rest of the decor.....
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)