Under Alabama law, that is a VERY dangerous play and you could end by losing money.You also cannot sit back and let him build the house and say "Thanks."

They look solid and well built, it's the high crime rates and the developing area thats my worry. 

million in addition to their investors (who expect a reasonable rate of return) by keeping the rental rates at a fraction of the market rate?

In 2020/2021, when rates were at all-time lows, this area was super hot, like most other Atlanta markets, and investor demand was high.

Say Income tax rate is 25%. 

The deal doesn't work as well with higher interest rates.

Another option is to estimate value based on potential income and market cap rates, which can give you an investor’s perspective.

2 years to build a house is crazy.

Here's a fundamental explanation to get your juices flowing:Assume a house costs $200,000 and rents for $1,500.

It's mostly a joke.I think it did good - the influencer who opines regularly on cap rates, interest rates, the Fed, inflation, and is generally an economist, or even a bit of a philosopher, probably does alright!