Roofing estimates for flat roof replacement -- materials?

Hi all!

Our flat roof for a 300square feet room (new addition) was installed using shingles. After a year, it leaked. The same constructor came back and put a layer tar over the shingles and some roof fans, telling us that would fix the problem and charged us $1500. Another year passed, and we had another leak. Long story short, we are getting estimates from other roofers. One recommended doing flintlastic, and another recommended fiber tite. Which one is the better material? Both are around the same price. The fibertite roofer told us that the tar is going to eat away our shingles, is that true? We don’t know anything about roofing, so hope you all could help me. Thank you all!

IMO fibertite is much superior to flintlastic if installed correctly. And no, the tar will not eat away your shingles but it is not a proper fix.

Shingles on a flat roof? your kidding right?? if your not, you got the complete wrong system on there…

Is it Totally flat or just has a low slope? I use GAF self adhered Liberty Cap Sheet on low slopes and have NEVER had a single problem. It is not designed to be installed on a totally flat roof however, especially if there is ponding water. We get these type calls all the time and this is the solution if there is any slope at all.

completely wrong system on there…