This idea comes from one of the Usborne Book of Arts, which I have referred to a lot over the years. The important feature is that students first paint the rectangle shapes, and lastly draw building details on top. The result tends to be so much more creative than if they had drawn the buildings first.
1. Student paint a series of large rectangles for buildings across the paper, leaving a bit of room on the bottom and the top. Watercolor paint on watercolor paper works best.
2. When complete, they are to paint a background layer of buildings that are all connected, preferably with just one color.
3. A sky is added with some very watery paint that fills in the remainder of the paper. Let dry.
4. With a black Sharpie, the students trace their cityscape, and add lots of detail to the exteriors. I’ve had some of my best results with just direct black Sharpie tracing (no pencils), and if students draw something they don’t like, they can fill it in and just continue.