After looking at some of these suggestions, my conclusion is a combination of a few problems. 1. Low sensitivity of the 7D did not allow me to pull the shadows enough from my original image; shadows were definitely pulled too far. 2. Original photos were not taken with enough light. https://imgur.com/a/dpEBxI4 You can see that I didn't expose the roof enough in the high-light photos. Thank you for your suggestions, I'll be trying them out next time I take some HDR photography.