I did a couple of demonstrations of how to capture the shadow patterns quickly before they changed. It's an easy procedure. First, lightly sketch in the shape of the building. Next, outline the shadow patterns, making sure to simplify them as much as possible. Then block in the shadows with a mid-value, and finally note with light paint (or pastel) any little bits of light that show up in these simple shadow masses. Sometimes these little bits of light are an edge of a shadowed window that catches the sun.
As my demonstration was about to begin, a septic service truck noisily pulled up just to one side of my subject. It's funny how these things always seem to happen! The fellow driving it had to spend some time searching for the septic tank with a shovel before he could start pumping. Ironically, we both finished up our tasks at about the same time. I'll add "septic service truck" to my list of plein air challenges!
Here are my two 5x7 pastel demonstrations.

