The stone detail is very important to get right as that is the main detail that contrasts with the brick work. There are many images online of portland stone so I download a few and referenced them to this image I took of Maple House:
From this image I download these images which I could see being the most simular:
I ended up using the last image as I feel it was close test to the reference image:
Architectural Visualisation/ Cinema 4D 