Looking for Flat Roof Experts!

A lot of roofing companies don't do flat roofs. It's tough, unpleasant, specialized work. 

I used Tico's Roofing to replace the roof on my house - about half regular shingles and half flat. They had to scrape off decades of membrane plus layers of plywood, some of it rotted and needing replacement. It was a big job with lots of challenges - extremely irregular roofline; lots of chimneys and other penetrations. I had multiple leaks - had to distribute buckets whenever it rained. 

The work was done in September 2016 and I sold the house in December of 2019. No sign of a leak after the roof work was done, and there were some good storms in that time.

Tico's has done probably half of the roofs in Maplewood/South Orange. They're a long-time, well-respected business. You might also check with R&G, who has done the other half of the houses in M/SO. (Exaggerating, but not by much.)

May not be what you are looking for, but we have a 2nd floor deck that is the roof of a room below. When we moved in it was a tar roof with a wood deck built over it... and was leaking into the room below. We quickly changed it to vinyl decking (https://duradek.com/vinyl-decking/vinyl-decking-applications/roof-decks). It mostly works well, lasting about 8 years. But the railing screws are the weak point, and it required the installers to come back and fix the installation.

ETA: https://weatherdek.com/ and https://tufdek.com/ seem similar, and appear to have railing options that don't screw into the vinyl.