Some building kept completely modular. So you could move things around to fit the scene and place where it was needed without worrying about the height and width.
Materials were made in substance. They were recycled for the buildings, with only little tweaks made, like changing the colour and normal. Some of the materials were turned into trims for the buildings the rest were seamless textures.
Planes were created on fit the edges of the buildings perfectly for the decals, as some building were at awkward angles.
Decals were uved like trims – little pattern details were sculpted onto a plane, the plane is then placed on top of the buildings. Some patterned details were placed in the material trims