I have a $2M building I bought for $935k, 3.5% down. 

This will cut down significantly on the issues you may have down the road with communication, paying rent on time, caring for property, etc. 

Class A- Brand New buildings with lots of amenities, good infrastructure & locationClass B- Building are usually older; priced less than Class A & need some updates/restorationClass C- Oldest buildings (20+ years); need significant maintenance; less attractive locationsWhere things become subjective is an older building located in a neighborhood that's changing for the better. 

Speed of building a portfolio (Cash-on-Cash return is a factor here)?

I highly encourage all my tenants to keep open communication with me about any struggles to pay rent, and generally they do.

Because it's easy to get a license, but it's hard to build a business.Who is going to list their home with a guy who lives in another country?

The question behind the question is that I'm trying to figure out how to communicate with property owners that have under-utilized assets.

It's likely they may even use data of SFH with similar lot and building square footage.

If you have the sellers, the buyers will start reaching out - it likely wont work for some of them and then you can ask what they are looking for and build relationships that way.

Looking for building from 1950-2010 anywhere from 10-100 units.