how to join garage roof onto existing wall

[toffee]

We need to replace our garage roof and whilst someone is going to help us do it, Im looking for advice on how to do it.
The old roof was corrugated panels sitting on wooden beams (breeze block walls).
The roof had to come off when an extension was built on the back of the house, as originally the garage stuck out further at the back than the house. Now, the house sticks out further.
So, what we are left with are breeze block walls and the beams still intact as they run parallel to the house and were untouched.
However, there is now a pipe running down side of house from upstairs bathroom and a downstairs toilet .This pipe is in the middle of the garage.

Can anyone advise how to 1) put a roof around the pipe?
2) best way to join the roof panels to the house for a waterproof join?

 

[nstreet]

Is the pipe a rainwater pipe, a vent pipe or a waste pipe for the bathroom?

What size is it?

 

[toffee]

its a waste pipe coming from the upstairs. I m not sure offhand what size pipe Ill have to go outside and measure it but it has to take a toilet sink and shower water. Also, the toilet and basin and washing machine, which is the room directly below.
Im going to go out now and measure it.

 

[toffee]

The sink and shower pipe join the big one above the roof level so its just one pipe that goes through the roof and its 14inches circumference and about 2 inches off the wall.

 

[Nige F]

Expensive.....lead flashings, Cheap.........Flashband