I built an approximately 8 x 6 structure that extended just above the cloud layer. It is important to note that the roof as it appears from inside consists of only a few blocks. As I looked up to the roof of my building from the inside, a portion of a cloud was passing through my building, just below the roof itself. I only realized it was a cloud, however, until after it had passed, because instead of rendering those few roof tiles, coated in fog from the cloud below, it rendered straight through to the night sky above, as if the blocks weren't even there! The cloud itself was rendered properly. As the cloud passed, the blocks were revealed once again, properly rendered. But to put it shortly, for a moment I thought there was a hole in my roof!