EDPM is cheaper and doesn't last as long. Make sure your builder knows how to do flat roofs, poor workmanship can make them a nightmare and hold water. If you have trees in the area make sure to clear the debris off at least twice a year because the tannins can damage the roof, bugs can dwell in it and damage the roof, and plants can take root and damage the roof.
Are you thinking fiberglass sheet like corrugated tin? I am talking about GRP roofing material that is a competing product to EPDM. Everything will eventually crack and fail, fiberglass lasts longer before compromising failure.
Necropost, but did you choose one in the end?
I've just had to DIY an EPDM, and honestly...It's not horrible to work with, and if done properly shouldn't have any issues.
Sounds good to me. If you're getting a builder to do it, you're almost definitely better off with whatever system they're happy using.
Everyone will have their preference that they feel most comfortable with.
Honestly, I reckon it's 6 of one, half a dozen of the other. Over 25 years, it'll probably do the same job.