I know that people are doing really well with short term rentals in our area and given the changes to the additional dwelling units in CA that may open up some additional possibilities. 

They will only lend on one unit dwellings so if you have a 2 to 4 unit property you'll have to use a portfolio, commercial or private lender.I hope this helps and have a good one.https://selling-guide.fanniemae.com/Selling-Guide/Origination-thru-Closing/Subpart-B4-Underwriting-Property/Chapter-B4-1-Appraisal-Requirements/Section-B4-1-3-Appraisal-Report-Assessment/1736875861/B4-1-3-05-Improvements-Section-of-the-Appraisal-Report-10-24-2016.htm

I was wondering if anyone had any experience or was planning on building or converting existing living space into an extra unit in California, or any state for that matter. The reason I specifically mentioned CA is be...

@Stephanie Choi builders risk covers vacant properties, covers the dwelling (house) even though its under construction, materials, fixtures, and equipment.

With Tampa rents increasing the highest in the nation YOY more than any metro it might be the way to go for an additional source of income.Below is some of the basic requirements to get a Tampa ADU building permit:Accessory dwelling unit.

What can be done to get the city to recognize it as a legal dwelling, or that it even exists?

If you have the house at this point, no reason to dwell ;) Just starting running!

All my rentals are single dwellings but I'm in the market for up-to a 4-plex.With 5 or more units, you'll need to pursue a commercial loan.  

I have looked into the same issue as it relates to Accessory Dwelling Units in Portland, OR.  

The landlord shall not commingle such moneys with any other funds of the landlord or hypothecate, pledge, or in any other way make use of such moneys until such moneys are actually due the landlord; or(c) Post a surety bond, executed by the landlord as principal and a surety company authorized and licensed to do business in the state as surety, with the clerk of the circuit court in the county in which the dwelling unit is located in the total amount of the security deposits and advance rent he or she holds on behalf of the tenants or $50,000, whichever is less.