Renowned architect, my professor in Europe, maybe 2005. Flat roof in EU was a little like Parapet walls in NZ. Or "No-Eave" design!
He explained that all his large buildings in Germany, all his flat roofs work 100%. Outside Germany some seam to leak! And than he showed us the photo of a contractor on the roof, distributing gravel over the waterproofing membrane on the "flat-roof"... WITH A STEEL RAKE!
As a result of lack of workmanship and probably guidance for labour, these guys didn't have the proper tools on site and ended up damaging the membrane with a gravel rake they are used to when doing landscaping.
But.. everyone blames the ARCHITECT!
One thing NZ does well is share the experience and knowledge. Lets do that more.