Since I'm aiming for "functional wargame terrain piece" rather than "beautiful scale model", I'm generally happy with the way this is turning out. The trick is going to be ironing out the method so I can churn out a dozen or so of these to make a half decent sized slum district.
Looking at this prototype has made me rethink a couple of things. The ground floor doors and windows definitely need to be pushed out 5mm, so that the doors are closer to the side walls and the windows are further apart. I've also reconsidered the pavement width - I had been thinking 50mm, but that's way too big for this sort of building. I'm torn between having free-standing pavements put on top of a base road surface, with the roads being formed by the spaces between pavements, or going with a fully grid-based setup of 150mm terrain squares (with a road being 100mm of cobblestones flanked by two raised 25mm pavements.) Right now I'm leaning towards the former, since it gives a lot more flexibility.
And though I'm thinking of this in terms of VSF GASLIGHT terrain, exactly the same thing will apply to the modern city/zombie terrain. I most definitely won't be using brick paper for that, which removes one level of fiddleyness.
Next up, a trip to Homebase in search of the elusive cobblestone embossed wallpaper.