I have a double level garage that is pretty new and has about 750 sq feet of living space.  

A listing agent provided him with a brochure stating the house had 15,000 square feet of living space, but county records said the residence actually was only 9,434 square feet.

I ask a number of questions like what is space rent, what are other expenses like garbage, water, and electricity.

Maybe what you think is sketchy is actually normal in the hard money lending space. 

I am able to build 2 units roughly around 800-900 sq. ft. which is about 1600-1800 sq. ft of livable space which I am able to find market comparables but obviously without the same lot square footage.

I am assuming the tenant would be responsible for space improvements. 

Whether I am there or not, they have a large space that could be used to meet in.  

Car storage is in fact in very high demand as the economy improves people are buying more toys with no space to store themI built 107 storage condominium garages in So Cal.

It's mostly offered in the commercial space with gse lenders. 

The FNMA condo guidelines are all here  https://www.fanniemae.com/singlefamily/project-eli...Condo projects and properties which don't meet Fannie Mae and Freddie Mac warrantability standards are known as non-warrantable.Non-warrantable condos are more challenging to borrow against.Typically, a condo is considered warrantable if:No single entity owns more than 10% of the units in a project, including the developerAt least 51% of the units are owner-occupiedFewer than 15% of the units are in arrears with their association duesThere is no litigation in which the homeowners association (HOA) is namedCommercial space accounts is 25 percent or less of the total building square footageWhat  you want is lender that will lend on NON warrantable condo project.