hole

I need to drill a large hole in two skin wall made of breeze blocks. The hole needs to be at 45 degrees. This is to fit my twin flue chimney through the wall (5inch plus twin skin), so it can be fitted to the external wall. I was thinking largest drill bit I can find, possibly 12mm dia. fitted...

(ignore if want) So basically I've moved into this house and I've been given this room. Since I'm mostly free and finished High School I wanted to do some work on my room. -Is there anyway to fix these holes or fill them in if so what tools would I need to use and how would I fix it.