88 unit value-add Deal question

[James Wheelock]

Okay so my fiancé and I tackled our first deal which was a four unit that cash flows great for us now. Since then we watched @BrandonTurner talk about approaching complex owners on one of the webinars. So I decided to pull the trigger, and did a small mailer to apartment complex owners in my area. Low and behold, it freakin worked! I got a call from an older gentleman who owns and self manages an 88 unit he developed himself. I do believe he has taken a liking to us and may sell to us in the future. Here's my question. If I were to approach him with a value add deal proposition, how does one accurately determine what this commercial property is worth as it sits, and also the ARV?! I mean I know my market numbers for small multi family in my area. But this is a very new complex in a great location that brings in gross rents of ~67k. Wouldn't know where to begin with that animal of an appraisal.