Thanks Relic,
The buildings are made of what we call in the UK electrical pattress boxes and blank plates.
I wanted a pre-fab feel to them as if they are shipped in bulk via a cargo ship and then the owners/occupiers can customise (pimp?) them for their own purposes. Hence the various colours.
I don't actually do any shading as such. I use a black undercoat and then use cheap acrylics (Anita's Craft Paint). It doesn't much pigment compared with the likes of GW, Vallejo, etc so the black shows through so I just build up layers of paint to reduce the darkness. Then just one quick drybrush of a paler colour to highlight.
[I use the same process for my figures too.]