Soil stack diversion?

[Knoxy]

Hi all, I am new to this so please forgive if doing it wrong!

We are doing a self build extension to the back of our property and the existing soil stack is against the back of the house, this means it will need to go through the roof of our new extension, the roofer suggested diverting the stack so that it would have a bend on it and then travel along the wall sloping upwards horizontially inside the ceiling of my new kitchen and then venting outside at the side of the house.
Can this be done safely e.g no escaping smells and are building regs needed.

 

[seco services]

need more info than that.

take it its a single storey extension ?
what go's into the stack above where you want to alter its angle ?
what are the lengths you plan on running it horizontal ?

why can't the roofer just put a soil pipe flashing on the roof ?
is the roof flat or pitched ?