Above Ground Drainage Engineer

I am looking for a qualified drainage engineer who can provide some advice and help design a slightly bespoke above ground drinaiage system for a bespoke new build single home. It has a flat roofs as its a high-quality design in a conservation area. I am looing for good and discrete products that can be used for the roof penetration, and potentially minimising them through air admittance valves etc. I am an architect and looking for specialist drinaiage design expertise.