Ensure it is up to code.

I tried looking on Redfin for comps but I wasn't seeing any multis in that zip code.

The garage was converted and added to the living room/dining room area with a separate laundry room and all done to code. 

I live in grand junction Colorado with the first 3 digits of my zip code that begin with 815.

And then there's building code compliance - how hard is it to do, especially for a foreign-based design?

Currently studying my States Building Codes in preparation for the Contractor exam. 

Code requires access to your floor system so in pretty much any semi-modern home there is access.

Should I get an estimate from a home builder, see the zoning codes for the area, etc?

However from what I've seen it takes about 300 signs to get a contract and you'll want to keep putting new ones up each weekend because code enforcement will take them down.

Here is a link to the code that reads as such: IN CODE Section 25-34.1-3-2.(3) section 11 of this chapter;no person shall, for consideration, sell, buy, trade, exchange, option, lease, rent, manage, list, or appraise real estate or negotiate or offer to perform any of those acts in Indiana or with respect to real estate situated in Indiana, without a license.- See more at: http://codes.findlaw.com/in/title-25-professions-a...Here is a link to all Indiana codes for anyone interested: Indiana Real Estate Commission Laws and Regulations.With that being said, if you're considering a manager/management company here in Indianapolis, you can check to see if they are licensed here: Indiana Professional Licensing Agency.From the IPLA site, you can search both an Organization or an Individual.