Daniel,
Have you considered knocking out a scratchbuilt wall panel the exact way you want it, giving it some depth, and casting your own in plaster? The building you have there is cast like a castle wall, making it an easy concept to replicate if that's what you want. Hydrocal is easy to work with and good for the thick stuff, and suitable for a flat that's braced by a backdrop.
Otherwise, N Scale Architectbs Model Builders Supply line has brick sheet that is 11"x14" (with the flat border of each sheet, it's closer to 9.5"x12.5" - orientation running the longer dim). AFAIK, that's the largest brick sheet available for N and is suitable for curtain wall constructions, and it's got good masonry detail. With strategically placed butressing elements or drain pipes to conceal the joints, you can go pretty big with these sizable sheets. The brick sheet also comes in different bonds for different era-d buildings/additions.
Ed,
You come up with drawings and I'd be glad to help build your Crown complex.