I tried to find pictures of snow drifts at roof top structures showing wind shielding and had a lot of difficulty. However, for a whole building you may have better luck. I would think snow drifts would be your best bet for showing wind shielding.
What kingnero said, a lack of drifting snow can show where wind was unable to reach a location. You would need a picture showing drifted snow on the shielding items and the lack of drifts on the shielded structure.
