Newbie, BRRR, Multifamily, how the heck do I calculate ARV?

[Tony Spencer]

First time poster here.  Hopefully this isn't too long or specific,  but here goes..

I want to try BRRR investing with multifamily. Cash flowing multi family doesn't pencil out in my area (Seattle), so I'm searching high rent/price ratio markets nationally. I've found tons of interesting properties that appear to cash flow, in my price range (600k)(I've got $150k cash). But how do I find comps for ARV?

I've looked for sold properties on Zillow/redfin/ect. But finding it very difficult with apartment buildings to find comps. 

What should I be doing differently? 

Respectfully, Tony