John, what type of roof membrane do you want to install? There are numerous flat roofing options including TPO, PVC, EPDM, Modified Bitumen. TPO, PVC, EPDM are considered single ply and are installed either ballasted, fully adhered, or mechanically attached. Modified bitumen is not a single ply, though I have hered it referred to as such on numerous occasion. Modified bitumen requires multiple layers, most often a base sheet and a cap sheet but sometimes a mid ply as well. Modified bitumen can be installed self adhering, cold process applied, or torch applied.
Personally the only DIY roof systems I recommend are self adhering modified bitumen or EPDM. TPO & PVC are my preferred membrane of choice but require specialty tools. I would never dare recommend anyone use a torch that is not properly trained.
Sometimes the savings that comes from doing it yourself can be blown away with one mistake.
The information found in this post is not to be considered legal advice. All information should be considered relative, not specific. Never attempt any repairs you are not comfortable with. Always maintain safety! The author of this post takes no responsibility for any losses that occur. Use at your own risk.