How do you evaluate/value 5+ unit properties?

[Shamus Quirk]

I found a 6 unit property that I am interested in looking into and I know 5+ unit properties are valued based on their income and not so much on other comps.  What do those numbers look like?  Is there a formula that involves multiplying the gross rent?  How does that work?  What do you do that may be different from other investors?  Thanks for your input!