How To Show Volume Using Just One Board

There are random lessons learned daily that can be applied in your art. Case in point: I just finished painting the bathroom and needed to add a shelf. (I want to free up some wall space for a water-themed painting, to come.)
This is a very old crooked house. But that fits perfectly, I thought, since I don't cut straight lines either. My technique is to eyeball it. If it looks right, it is right. I've heard there are people who must measure everything for precise placement.

'The downstairs bath with fish'   (shelf top left.)

Not me. So I chose a board from the barn, cut it, painted it, and placed it over my stacked washer/dryer.
The board was warped as well. Not only was it uneven in the space left to right and front to back: it undulates too. So much visual movement in a small space. 
But the surface lays flat enough, and that's most important. It holds the all the laundry accoutrements fine.