I'm trying to build out a robust deal analyzer/performance tracker spreadsheet for small multi-family and am trying to think through useful metrics.  So far I've built in:

1. Initial Cash-on-cash return.
2. Internal rate of return - I have a way to project over a 40-year period and a way to compare to actuals as time goes on so I can see how I'm trending compared to initial analysis. I also have this calc split into an IRR without sale (based strictly on cash flows) and the IRR if I were to sell in that particular year (cash flows + sale proceeds).
3. Return on equity - similar to how I built out IRR, actuals vs projected and then splitting again into if the estimated property appreciation were included in the calculation or not.

I'd like to add a "Cash-on-cash over time" calc, but I'm not sure how exactly to do that, or if that is even a calc that matters.  It seems like it should matter given it's a main metric I've used and is a main metric other people look at to evaluate an investment.

Calculating the initial cash-on-cash is straight-forward (net cashflow/initial outlay), but do you just take each year's net cashflow divided by that same initial outlay every time?  Or what other expenses do you add to the initial investment for the calc?  I assume you don't add the debt servicing since that's accounted for in net cashflow (or would you?), but would you add, say, the cost to replace the roof?

Besides the cash-on-cash calc, what other metrics have people used or found helpful to either evaluate a deal or track it's performance over time?