I got this idea from another blogger but back when I found it I didn't write down where it was from. So if you posted this...thanks!
My JH students went on the computer and each found a city skyline to draw. Most students worked from one single photo, but some pieced a few photos together in their drawings. Students drew on gray paper and then added shadows with black and highlights with white. The middle grays were left gray or lightly shaded with white or black. I think they turned out well!
Here are a few examples: