This doesn't account for lease-up costs which will vary based on what the absorption rates are in your market. 

The reports will have sales comps, cap rates, supply/demand, market absorption, etc.

An investor-friendly agent can educate you on absorption rate, average days-on-market, and other variables you'll want to take into account.

Usually price.If the absorption rate is pretty low, you'll want to react quickly so you're not accruing empty days on market.

I know some of the new construction east side apartment syndicates are not doing well.. in that they can't get the dollars they wanted for their new construction units and absorption is not as good as it was a few years ago.

They started asking out too much for rents after rehab and the absorption rate was slow ( absorption rate is how many units you are leasing up per month ).

Find out the absorption rate of properties in that area and what they are selling for.

If you see strength in those areas, then you may project higher absorption and increasing rental rates.

You could treat it like a new project and use the local absorption rate, if one can be determined.

Obviously, markets with great positive market absorption where average home costs are 400k and higher require a different mindset than rehabbing most of the country.