How do you get After Repair Value for a 4-plex that needs rehab?

[Tim Richardson]

I'm looking at purchasing a 4 plex that needs extensive rehab in Salem, Oregon. Seller is willing to short-term finance while I use my cash to fix up. But how do I determine ARV on a 4plex so I can ensure I can get my cash back out as I can at refinancing (kind of like the BRRRR method)? Thanks!