Let me know if you need any additional help. Feel free to reach out to me directly at
Prudential California Realty
Beverly Hills, CA
anywhere between $800,000 to $40,000,000 or more. Having said that, on average somewhere between $150.00 to $300.00 per square depending on the quality of the materials and the square footage of the house.
I do suggest you contact an architect first, I'd like to refer you to one with 30yrs experience, she can give you 3D CAD designs too. Her name is Cheryl Williamsen of Paradigm Design, you can reach her at 714-381-3459 or send her an email at CWilliamsen@ParadigmDsn.com. She does have contractors & subs you can work with to complete your project too. She knows all the ins & outs of working with LA county for your plans & permits.
Shoot me an email directly if you'd like to talk to me some more. I don't look back on this same Trulia thread for answers posted after mine.
Realtor Since 1996
Main Street Realtors
Contacting Contractors in the area for estimates would be the way to go.
Probably an Architect first; and he could recommend a Contractor.
Good luck and may God bless