Without factoring in tax benefits and principal pay down, you're $1800 ahead of the game by house hacking.

The "fine print" here is fairly sizeable upfront fees and high interest rates, relative to a traditional construction loan from a bank.  

Those factors are more critical in a fix-and-flip scenario where you’re focused on resale to an end buyer.

You'd be surprised, sometimes there are buyers who just want to own a piece of land, even if it's not the most desirable and of course price is a factor.

Pull comps, if you rent it for 1500.00 you are cashflowing 120.00 a month with all the info you gave me and including fees except if you take any fees on (water/trash etc.

You can always charge an air and surface scrubbing fee from their security deposit after they've moved out. 

Furthermore, I have an additionally factor of safety of 1.4-1.6 which means I say it's capable of only 70% of what it's actually capable of.  

Perhaps slightly higher from an alternative lender but definitely not from a credit union and expect much higher fees.

In my devious mind, I thinking like you that I hire a parking attendant, install gates and charge an entrance fee if I bought it. 

Labor/material are going to be different and need to factor that in4) new roof, new HVAC, new water heater, ac panel, replacing plumbing to PVCThese are very variable, if you are getting this from a licensed guy to do it and unlicensed.. is it a big shop or a local shop doing it, is the GC doing it they will put some money on the top so it will be more money5) framing (creating new bedrooms or baths)I would get all these quoted from a good couple of licensed guys and unlicensed to know your numbers to cents