How to value a multi family apartment building

[Amy Ranae]

Hello BP Friends!

I'm looking for a 10-30 unit apartment building in my market place by pulling the tax records of buildings with this many units, then looking them up and doing some research before finding the owner and reaching out for a discussion. 

Here's my question, if I know what they are getting in rent, I know I should be able to figure out what the price should be. Grant Cardone talks about this all the time. However, since I haven't done it really yet I'm looking for your help.

So can we practice together? 

Let's say it's a 10 unit building of 2br 1ba apartments that currently gets $900/mo for a unit. Without knowing operating expenses, how would you establish a guesstimated value? 

Assuming 9k/mo income = 108k/ year minus 10% (vacancy? Cap ex? what rate would you use?)  now we are at around 97k/ year income. 

Where do I go from here? 

I'm planning a 20% down commercial loan, I've got a lender. But want to start practicing on some deals in my spare time. 

Thanks!