He says he can buy a new metal building kit of the size he needs for 30k....no slab and not constructed...and he is being told 700k total price to custom build but they need the architect building design with lifts and oil storage etc and civil engineer site plan with drainage to give a hard price.

The more loans (and loan size) and deposits you bring to a lender the more excited they get.  

This is mostly due the size, as a lender we are qualifying the building's ability to repay not your personal ability to repay.However, if you have good income getting a regular commercial loan secured by the lot shouldn't be too big of a deal for a community bank or portfolio lender.  

I suggest getting the going rate for contruction with like materials and craftsmanship per sq foot. multiply that by the size of the structure to come up with aprox replacement cost.

Unit sizes, unit rental prices, current occupancy, competition in the area, condition of the buildings, taxes, etc etc etc.. 

Doubled size of concrete patio and added concrete walkway from driveway to back patio.

For example, I was at a networking event where the guest speaker was the owner and live-in manager of a decent-size apartment complex.

Just be aware with deals of that size come larger problems - I am in a position with my bank and other business that I was able to access some cash to do a major unexpected re-roof (yes, it's my fault that I missed the urgency of that in due diligence - I thought I would have a few more years).

Meaning, a 30YR fixed often can get you the same rate as a 5YR or 7YR ARM, depending on the deal (credit, DTI, loan size, etc...)A 10YR ARM will never beat a 30YR fixed with rates the way they are, so that would be off the table. 

Loan size?