Party wall rainwater coping gulley thing conundrum

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Looking for advice or any thoughts. I live in a 70s mid terrace house with a shared RWP that drains my side of the fence. I want to extend the full width on the boundary making new party walls. The extension will be with brick walls with coping and the roof will be low pitched with a gutter.
I'm trying to decide how to deal with the RWP route. As I see it there are 3 options:

1. RWP stays in current position, so goes inside the new party wall.
2. RWP dumps onto new extension roof.
3. The new extension wall with the RWP has a gulley/channel/aqueduct sort of thing to take the water to a downspout at the end and into new drain. The other wall will have standard coping that matches.

My logic says option 1 is not ideal as it's introducing water into the wall - potential for issues? Awkward access for rodding if needed. Not really possible to harvest the rainwater water for the garden this way.

Option 2 not ideal either as new extension roof and gutter need to work harder - possibility of issues with that as it's a low slope due to height restrictions.

Option 3 seems like it would be practical. There are no trees nearby for leaves clog it up. Relatively easy to clear it. Probably the most expensive option.
Lots of examples of this as a water feature but I can only find one example of it being done on an exterior wall (first 2 pics). So I guess it would be a bespoke thing?
Is it more common than I think - any other references?
Would this be a good way to go or am I missing anything?

Thank you for reading
 

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Thanks for the replies. I think the pitch will be 7° so almost flat with the height restriction. Either standing seam or GRP, and the extension roof will extend 2.8m. 5.5m width.
The RWP will be coming from the roof above with a total (shared with neighbour) area of about 50sqm. That roof has a 24° pitch if that is a factor..
 

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