So if you model one of your own, do it after the TAR form.

The billing model incentives are counter to the best interest of the property owner; There is a financial incentive for property managers to churn units rather than address tenant problems.Most of the "professionally managed" properties I look at to buy are not nearly as well maintained as owner operated buildings and the work is shoddy.

If you look st the model of supply and demand.

I have seen one that ran the entire perimeter of the lot, with T's that would have been for faucets at various points that went all the way to the road (Maybe model T's needed a lot of water?

Conservative leverage could be a good model for you.

Be sure to do your DD on the operator and understand their business model before diving in.

You might consider running this model as a flip to see if it makes sense economically. 

- Pension Real Estate AssociationBerkadia - 2019 National Apartment Research Report - click on "Forecast 2019 Book"

It's a business model - it needs to make sense.

So that's where you've got to examine your own model and needs.