I like the TPO systems, another great commercial roof, available for residential.
Couple things, Old dog gives great advice, been at it long enough to know better.
First thing is to talk to your local Building Dept as to what is allowable in your area. These Cali folks have a whole different set O rules than the rest of us.
You folks have Quakes, which should not matter on a roof, unless you are fixing structure.
The other thing is fire, rubber and vinyl roofs may have to be certified to withstand certain things. That is why rock ballast is on some older roofs.
Ask what they want to see before you get any estimates, then you can compare aples to apples ,, so to speak.