The economic risk and return theory is generally applied to building design as well. While risk of leaking is higher, flat roof can often gain higher usage of limited building platform, achieve a better view, achieve desired exterior looking, hide unsighted features, bring more light into interior space and so on.
As long as well designed, well built and well maintained, just as any other exterior features, flat roof with internal gutter can be well performed or even out-performing many other type of roofs. It is problematic only when either design, or construction or maintenance side has got any problems, such as no consideration was taken by the designer for future maintenance and replacement, incorporating overly complex junctions, substandard materials being used during construction, poor construction workmanship, minimum or no maintenance by occupants and so on.
Flat roof incorporating internal gutter is a building element, which inspectors should keep good eyes on rather than simply relying on inspection tools only. It is a typical feature, which to be assessed from design, construction, historical and current performance, likelihood of future major issues, expected serviceable life and other perspectives. A competent building inspector should deliver a lot more comments than simply stating “leaking or not”.