A site that large will most likely need an architect, civil engineer, traffic consultant, impact engineer, attorney, and perhaps a wetland engineer if there is a creek. 

Architect?

My architect was ok (and friggin expensive) so PM me if you want his info.

These issues are often bought up in opposition to granting zoning variances.I had run into these problems and employed the use of "expeditors" who are often architects by trade, but not a requirement, and would help if they know local zoning officials who has their own unwritten rules unavailable to the public.It was many years that I used them, but they charged $150 to do a walk through back then and go into building codes as well as zoning issues.

I am an architect so have been experienced in real estate and construction for 12+ years.  

There's many companies in southern California that are one stop shops where they have architects, engineers, etc. if you do a search.

I do have construction experience, outside of being an architect as my day job, so i know i could do good work and for cheap.

Slabs under garages are often thinner than under the main house.You’ll need an architect to make sure you have adequate foundation to support the weight and configuration of the new unit. 

I have an architect who is ready to draw up plans but I still would need some sort of estimate for the cost of the build being that I am using private money to get this deal done. 

Architect - Needs specific experience with storage unitsFinancing options - bridge loan, agency loan, etcGeneral Contractor - Experience with building storage unitsIf you would like to jump on a call with me for 30 minutes and ask me anything pertaining to real estate I charge 100 for half an hour.