Another way to get an estimated value of your multifamily is to compare it against other nearby properties that are currently on the market.

Can also call a couple local property managers and have them give estimates on rent estimates.

@Stephen Jones I don’t see any estimates for management or lawn care.

Simply point out the problems and present the sellers with the estimate to repair.

If the property is in a rural area and there's not any properties nearby, look online for "For Rent" properties that are similar to this one after it's fixed up...you can then look on the county GIS to see what their tax value is and extrapolate (guess, estimate) what yours would be valued at ARV.  

I am estimating $2500/mo vs $3500/mo.

If you have the deep pockets to pay cash, are familiar with the area and the property, and have enough $$$ to make repairs (estimate the worst case scenario), and the property checks off most of the "wants/needs" on your/your parent's list, go ahead and make your best offer.You could also call the listing agent and ask them if the seller has any special requirements that they would really like to see in an offer.  

In order of importance, I would rank the 3 steps as find buyers, learn to estimate pricing, find sellers. 

Repairs estimated around $10-15k.

It looks like recent sale comps are under $200k so I would make sure to check with a local agent or expert to verify the ARV estimate.