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.
DIY
For DIY - this is also a placeholder.
Some people report that fibreglass gets brittle and cracks. Thoughts?
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.
GRP yeah.
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.
Every builder I got a quote from recommended fibreglass over EDPM since we are going to have a roof lantern.
The builder I'm going to uses this system: https://www.tuffstuff.co.uk/
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.
Fiberglass can be smashed to shit by hail.
If hailstones EVER happen, you want a non-fiberglass roof, which you may well have to replace, after a storm.
Thanks. Not sure why the down votes.