The new flat roof systems being used at present are great.
Fibreglass and also EDPM roofing systems should greatly outlast the previous felt alternatives which are more prone to water ingress causing damp.
If I do go up on a flat roof (which is rare) I always try to walk along the wall plate (edge) as much as possible, by doing this the impact of your bodyweight should be minimal on the strength of the roof's supporting structure.