I very quickly made a simple building in Blender -- maybe it could be a three story office building. I just wanted a piece of repeating architecture. Nothing too fancy. I decided to render it out toon shaded with the edges in Blender. From there I was able to grab the flat colors and add gradients and some additional shading. No textures this time.
As for the original Blender setup I used a sun light and a hemisphere light to give it softer looking shadows.
The windows were made by using a gradient and then liquefying the edges to get a bit of distortion. The trees are painted using my tree brushes. Same with the clouds.