I've managed to finish off the building and get it painted. I added a spire made from the Adeptus Titanicus spires kit, which I think scales off quite nicely. Because the top of the building seemed a bit wide and empty around the spire, I added some little domes or blunt spikes that I bought at the local art shop. I'm not sure what they're for (they might be the tops of fences in a bigger scale) but they make good gothic adornments. Also, I used them on the roof of this house, so they'll tie the scenery together.
The painting was fairly simple, and I used colours that reflected the other buildings for consistency. Probably the most interesting bit is that I used a light grey-blue for the highlighting colour on most of the stone, instead of my usual bone colour. I think it works really well and I like the overall effect.