My career was a general contractor, so have a leg up on most in in terms of knowing how to get things built efficiently, economically and navigating through all of the code and permit issues.
Two partners and myself designed and built a $1 mil custom commercial facility for a company we were familiar with and leased it from 2000 thru 2018. We paid cash for the build (no loan), and took approx. $14,000 per month / $168,000 per year in rent for a total of approx. $3 mil total over 18 years. In 2018 The tenant exercised their purchase option and bought the place from us for approx. $900,000.
A $333,000 initial cash investment paid me approx. $1.3 mil over 18 years. I'd do it again.