How to make an offer on multi-family property that isn't listed

[Keith Richer]

I'm wondering if there are good methods for coming up with a purchase price (offer), as a buyer, for properties that aren't listed on the market: specifically multi-family?  My initial thoughts are to "reverse-engineer" an offer based off of a targeted cap-rate, cash on cash return, etc....but wanted to see if anybody has recommended methods for doing something like this.  Thank you.