But, since you seem to be implying very specific things, but without being specific.

What would you consider a good minimum profit margin?

Margins are often squeezed. 

It's been a long-time dream to do a new build and so I'm actively working to find land and begin the process.I agree that the profit margin you post seems very small.

i think its very property and location specific.

If you can save up for a slightly higher down payment your margin for success will be significantly higher.Also, I strongly agree with the "buy the worst in a great neighborhood, live in the worst unit of the triplex and slowly fix it up yourself."

Your specific variable expense assumptions are wrong, BUT you stumbled into them being correct overall.Also, you are approaching this correctly - entering in the numbers to generate a purchase price that meets your metrics:)

Just because you want to hit a specific number doesn't mean the market will meet you there.Great example of how Class C properties may appear like great cash flowing investments on paper - meaning fully rented, paying on time and normal levels of maintenance.

You take the div to pay on margin %, your sub 6%. 

However, you have to invest in specific communities where they are encouraging development.