Göbekli Tepe, Turkey.
Considered widely to be the first temple to have existed, it dates back to around 10,500 years ago. (8,500 BC) Although archaeologists first discovered the site in 1994, alot of it is still buried.
People like Ted Banning claim it was no temple, but an "ordinary" house, as he refers to the large amounts of animal bones, charcoal and other items pointing towards the site being a regular house rather than temple.
Chances are the roof was made out of wood, covered with dirt; the abandonment and rotting of the wood would've buried the site almost immediatly.
http://en.wikipedia.org/wiki/Gobekli_Tepe