Single storey gutter against pitched roof

[intamixx]

Hello,
I am in the process of building a single storey extension next to my neighbours garage (No.3), we are a detached house at No.1. I haven't started getting builder quotes in just yet.
Please see attached images of length of wall and front elevation along the boundary. I was wondering how the long gutter against the pitched roof would work.
It wouldn't be that easy to maintain as its along my neighbour owned boundary fence. I don't want an overhang gutter as I would like to build up a far to the boundary as possible.
Is there such a thing as a structural gutter that can be built into the wall?
I have seen images of hidden, concealed or secret gutters as attached, but are there issues with cleaning them? What would be the recommendation in this case?
Otherwise, I think the standard thing would be to build a parapet wall that includes lead flashing for the water to run down into a drain at the end of the building.
Although its not indicated on the front elevation plans, how far up would a parapet need to go in order to do the lead flashing?
Any advice is greatly appreciated.
Thanks.

 

[noseall]

I don't want an overhang gutter as I would like to build up a far to the boundary as possible.

For the sake of a few inches you'd rather have a permanent ugly headache that will be difficult to maintain and prone to problems unless it's done with a large degree of skill and care?
Could you not pitch the roof so that it runs front to back with a gable on the neighbours elevation?