I'm aware of the stepping problem, and will take steps to alleviate it.....

AS: Actually I had just finished to prototype for this late last night, but yes you are correct , subtle blurring and 16bit.

UVDan: I used a photograph of the front of a building. Then I make a layer. On this layer I start to select areas (like the stone face or trims) and colour them at differing levels of grey, depending on how much they protrude from the front of the building. In other words, the lighter the grey the more that part of the building juts out, and finally use black for the windows etc. Hope that describes the process.