This is a great project I picked up at http://alisaburke.blogspot.com/ She's got a lot of neat ideas that are super for inspiration. I believe this was under her April posts.
My 4th graders looked at St. Basil's Cathedral, The Taj Mahal, Italian cities & Paris cityscape's. We looked at roof shapes, patterns, lines, shape and color. Students used sharpies to draw in the layered buildings and then liquid watercolor to finish up. Love these results! Thanks Alisa Burke for the inspiration!