@Bing Lin - I would look for the office CBRE, Cushman Wakefield, Colliers, etc brokerages and ask the brokers what kind of leasing volume they are seeing, as well as appetite for area, terms, style of office, etc.  

@Lamont Marable find an investor friendly agent and you can get all of these questions answered for free from Someone that wants to earn your business.Adding units is extremely difficult if there is not already a fire suppression system in place or fire walls present.

The specifics of the deal and the appetite of the municipality usually dictate which path is best.

This cycle continues to suppress available rentals. 

Yes, you can use sources like rentometer and Zillow rental manager to try to comp similar rentals and see what the market appetite is for a comparable unit.

I called every lender in my county and asked questions so as to determine what their "appetite" for lending was. 

Ive been investing here for a couple of years and have found many different forms of investment properties to satisfy almost everyones appetite. 

You just have to check around to find which ones have the most appetite for that deal type.

Not sure if it matters, but the whole building and all units have a fire suppression system and other things needed for a commercial building since the 1st two floors are commercial, the city made us make the entire building outfitted with a fire suppression system and wireless notification.

Depends on your risk appetite too I suppose.