Optical illusion

On one of the few occasions when I have been allowed out of the kitchen, I looked across the valley at where our builder, Guy, lives. 
I was certain that there wasn't an extension with a sloping roof on our side of his house but that is what my eyes were telling me. Looking again, I realised it was the shadow from his terrace causing the effect of a sloping roof.
You can 't believe what you see......