Yes I'd not allowed for the downpipes on each side having different
amounts of water. However the roof that I'm wanting downpipes for is a
hip roof, and the spouting runs all the way around the roof. So in
theory I don't have to worry about the pitch.

I am not sure about that theory. Even if the gutters are laid level all
the way around (which reduces their capacity - and is not allowed in NZ
from 5.3.1 of the Clause E document?) the water from the "rainy" side
will meet one downpipe before the others. But this is getting beyond my
level of incompetence into "act like a politician" territory

There are wide eaves, so
if there is a torrential downpour the water can overflow the spouting
without a problem unless someone is standing underneath!

....especially if that someone is the BCO

--
R