Fibreglass or rubber roof?

[Spikeyplants]

We are re-building a garden room (4m x 11m) with a flat roof and lantern in the centre. What are the pros and cons of both roof options?

We went round and round with circles over this as we did our own roof on a rage kitchen extension. Various roofers quoted who insisted on only using fibreglass. We were going to use fibreglass but then read a lot about noise - cracking and banging etc where it expands and contracts. In the end we did a single ply liquid rubber which we painted on. Horrific job for a newbie diyer but very pleased with it!

I've been speaking to a few roofers (and a surveyor) recently who still advise 3 ply felt as the best option.

Thanks for the ideas. I never knew fibreglass was even a thing for a roof till this week.

My late FiL, who was responsible for many council houses in his area, told me 40+ years ago ‘ there’s no such thing as a watertight flat roof’.
Despite the advances in technology since that time, I fear he was correct.

We went fibreglass after the rubber roof we had leaked.
So far so good and we're 2 years in.
It is over the dairy in our farmhouse so expansion/contraction noise, if there is any, isn't an issue.

Why not look at a green roof?

@Daftasabroom- Yes, that would be even better IMO. Could you link some info in terms of what base you'd need for that? Is it rubber, felt or something else?

@Spikeyplants either would be okay. Whichever method is used, rubber, GRP or traditional 3 ply, if it isn't done properly there will be issues, just like anything.