My bathroom would benefit from an extractor fan but not sure how these are typically vented. The bathroom is the first floor of a two storey annexe at 90 degrees to the main roof and a slightly lower level, it has a pitched roof and a small loft space.

So would the vent point be best out of the top of the roof (ie. through the tiles) or by drilling through the triangle of wall in between the bathroom ceiling and roof?

I think the latter but just wanted to check as the bathroom roof is also being replaced.

Either would be fine.

You can get replacement roof tiles that you can attach the extractor pipe too or go through the wall.

Another option is to replace a section of the venting where the roof and wall meet.

One of those?

Ours is a fan recessed light combo that therefore goes up through the ceiling. It then goes out through a vent in the sofit under the gutters. Neat and tidy.

bails – yes pretty much like that only my roof will be flat slat type tiles rather than ridged ones. Is there a similar product for flat tiles and is that the best way to do it or is going through the roof as good?

Mad Pierre – that sounds good but is not an option as only the top 1/3 of the ceiling has roof space, the other 2/3 is sloping and so back to back with roof.

Here is the view from inside:
https://drive.google.com/file/d/0B2saEu3jEeMmOVM4c1NibEtDdUk/view

Ah right. Could just go simplest/most direct and go straight through the wall with the window?