Flat roofs in the rainy northwest for many years were a maintenance problem. The built-up asphalt roofing of yesteryear didn't last long and often leaked. The rainy northwest developed a style of pitched roofs covered in cedar shakes and shingles. It was beautiful and so were the roofs. But cedar trees were used up and the replacement was asphalt shingles. They are not so pretty and are quite a heat sink.
But things have changed. With the introduction of welded vinyl roofing the modern flat roof now comes with a 30 to 50 year guarantee. Designed correctly with ample drains the roof becomes the most maintenance free part of the house. We have numerous buildings now with vinyl roofs that have preformed well over the years. Cleaning up the drains in the fall is simple using a broom and dustpan. We like to include roof access hatches to make clean up even easier. Back up overflow drains ensure there are no leaks even if you forget your standard yearly drain check.
Another benefit is the typical color of the roof. Anyone who has climbed into the attic of an asphalt roofed home knows about the heat build up in the attic. Vinyl roofing can be any color. But with a white or tan roof the heat from the sun is reflected helping keep your home house cool. That in turn helps cut down on the heat island effect of dark roofing and streets in cities. Check out Santorini for the effect.
So, the modern flat roof is not the roof of yesterday. They are simple to maintain, last a lifetime and have no gutters to clean. Of course, you don't have the pitched roof as a design element for your home which requires careful attention to all the other elements.