Multiply that by my 15 residential rental units and that added up to super savings and gave me reliable information to go on.

In this case, a contractor who seemingly gave a low bid to get the job and then tried to multiply it by 5.

To follow up @Christian M.Here are the multipliers for finding the area accounting for pitch.http://www.browningrg.com/sloped-roof-pitch-correctionKeep in mind there can be a significant amount of waste in roofing.

Therefore the appraisal form, which is set by the Banks/Lenders are different than commercial property's, which typically place more weight on the income approach.The small residential income property appraisal report, address comparable rental data and breaks things down into items like value per bedrooms, value per gross building area, value per unit and gross rent multiplier, etc.

If you're year one, then sure, multiply by 12. 

Earn and keep, then multiply.

Then look at your time horizon for wanting out of a 2-4 unit and multiply... i.e. it's $1000/month to rent a place, or it's $500/month after you rent out the other units and you really want to be out of the 2-4 unit neighborhood in 3 years... 3 years (your time horizon) * $500 (the difference in renting vs owning) * 12 (since it's monthly) = $18,000... that means it's $18k better to buy the place.The numbers are all fictional, but the process is not.

I have experience with private equity and commercial M&A where we use an EBIDTA multiplier to value an acquisition.

Multiply that average comp square foot rent price by your property's or room's square feet to get a comp rental price.   

Capital Calls ( but we currently see this as a better option than forbearance)Come up with your estimated negative monthly cash flow then multiply it by 3 times and that is your capital call.