I used to own over a hundred rental units spread between duplexes, triplexes, and apt buildings.

It was only a good deal because we owned enough to justify a maintenance man and a secretary to handle it all.

Before 2008, they ALL made money.  We built a bunch of duplexes and it was very profitable with no money down - loan was based on appraised value.

Luckily we sold out in 2004 - just good timing - dumb luck.

Now, I don't think you can build one in most places and get enough in rent out of them.

I'm reminded of what my uncle told me when I tried to get him to invest in some duplexes:    "I'd rather chop cedar sprouts on a rocky hillside, with a dull axe, on the hottest day of the year, than deal with tennants."