Simple yet efficient. How did you make these little guys?
Drawing splines for outlines (long and boring process....)
move spline vertices to surface with a script,
extrude to meshes,
select top surfaces and move along z-axis for different heights (long and boring process....)
select all top surfaces and assign google maps texture
select all other faces and and assign a generic house face texture (50% random)
Here is a script which may be useful for big skyscraper cities:
Sadly not very helpful for building a small town in Germany.