I think I made a breakthrough. I was struggling to find a way to show the lighting on these buildings. My original idea of using Photoshop gradations looked to soulless. Tonight, after playing with pencils, charcoal and watercolor pencils, I decided that watercolor pencils will work best for me. I'll be able to control the tones and adjusting them in Photoshop will maintain an organic look. A rough test is below.
