I am a remodeling contrator who is moving into LA area. I stumbled across this site by pure hapstance, and I am NOT solicting business. I do not know any roofing contractors in your area, however, I do know that there are building codes that regulate how many layers of roofing may be on any roof at any time. In Atlanta (where I am moving from) the maximum allowed is 2 layers. Your best bet is to contact your local code enforcement office and ask them how many layers are allowed. This will prevent anyone from ordering you to rip off a new roof because you have exceeded the limits.
Best of luck to you in your search for a roofing contractor.