Both from age and elements and also tenants who tear things up.

New Roofroof age = 20 years or 240 months (guessingCost of new roof $7,000 (guessing)$7,000 / 240 = $30 per month (I added this in repairs)New Furnace (i do not know if this is 2 or 1 furnace)Furnace Age = 20 years or 240 monthsCost of new Furnace $2,500 (guessing)$2,500 / 240 = $10 per month (I added this in repairs)2 new Water Heaters (1 for each unit)Water Heater Age = 12 Years or 144 monthscost of new Water Heater $1,000 Each$1,000 / 144 = $7 per month for each water heatersWhat you guys think?

I wouldn't rely on the 50% rule as the expense ratio can vary - I've seen anywhere from 30% - 60%+ all depends on the product type, class, age/quality/condition, market, who pays utilities, etc.Generally speaking for B/C product built in the 60'-70's and 70+ units I've seen expenses range from $3,700-4,500/unit per year.

Find similar properties (what we call comps or comparables) based on square footage, lot size, bedrooms, bathrooms, age, etc. and use those as your ARV.Networking within a group is great, but ultimately the numbers you're analyzing will come from experience and will be situational (every deal is different). 

Use part of what you have for a down payment to the owner ( keep some in reserves for unexpected issues) see if he will carry the remainder of the loan for at least 5 years or possibly the life of the loan depending on his age and what he is needing/ wanting out of the deal.

I replaced three roofs on my properties over the 10 years at significant cost.(2) Do not discount the age of the housing stock. 

Found a place where the numbers were there but just too many problems between sketchy neighbors and the age of the house to pull the trigger.

Be sure to check the unknowns, roof age, hvac, plumbing.

@Solomon Morris greetings,Consider the age of the ductwork itself as well.

No need to get tangled up with someone who will have access to your pocket book and with whom you could potentially produce another living human being that would require time, energy and money.If you do this one step, you'll already be ahead of 50% of my tenants who got preggers/had kids out of wedlock and are now single parents trying to make it on a GED and a $10/hour retail job.P.S.