We have a rat INSIDE!

The house two doors down from us was cleared recently and the rather overgrown back yard was cleared as well. The rats who lived there have moved on. All the surrounding homes have had a problem since then. 
We thought we were being careful. We were keeping the yard as clear as we could. We put some bait down in places inaccessible to the local cats.  It was all done on the advice of the local council.
The front door was open most of the day while the electrician was here...wide open as they took things in and out. 
Ratty decided to move in. 
I thought I heard something yesterday - and then decided it was my imagination. If there was something it was in the roof, under the tiles. The cats have been up there - via the avocado tree, onto the carport roof and thus onto the roof. 
But this morning I discovered that Ratty was there. He has consumed a banana. What is more I came face to face with him. He sat there and looked at me. His expression said, "You stupid human."
No, I didn't scream. I was MUCH TOO ANGRY for that. He is  unwanted, uninvited, unwelcome and a filthy dirty PEST.
How on earth are we going to get rid of him? 
I HATE RATS!