Now this needs some explanation.Monthly Rent:  I get an idea of what the monthly rent should be by going to sites like rentometer..6: I multiply the monthly rent by 60% to take out 40% for the following: 10% vacancy, 10% property management, 10% maintenance, 10% property tax and insurance.

I just finished Avery Carl's book on Short Term investing and see the Gross Rent Multiplier formula as well as the Cash-on-Cash return formula.

This is the same thing as saying "the Gross Multiplier should be less than 8.33".

Find out what your city tax rate is and multiply that by your value and then divide by 121.25% x 110K = 1,375.00/12 = 114.58 per month in property taxes. 

As @David Krulac pointed out, the county assessed gets multiplied by a county specific common leveling ratio (CLR) that the PA Department of Revenue publishes periodically.For inheritance tax purposes, the valuation is for the date of death of the deceased borrower, so one would use the CLR for that county from that time period to establish the value.

The gross rent roll after repairs lease up will be approx. 1.5million/yr and the after repair value of this property will be 12-14million based upon comps or 12-15million based upon rent roll multiplier x8-10.

There are a few areas that you need to analyze: Operating Revenues, Operating Costs, Repair (one-time) costs, and Financing options.I would start by looking at the after-repair rental rates for both 2 and 1 bed units, multiply that out by your 10 (2 bed) and 10 (1 bed) units to get a total monthly revenue.Then, figure out the cost of repair per type of unit (~10-15K/unit depending on finishes and extent of repairs necessary) Figure out the cost of repair for common areas (exterior, hallways, parking, main utilities, etc).Use common metrics for operating costs (10% management fee, 10% repair, 10% vacancy etc, 10% capex, etc.)Then figure out the NPV of the deal with both of the financing options to see what works better for you.

Try working the numbers backwards to see if a property is worth  chasing;Take FMR * 12mo * GRM to find max FMV that a unit could still provide a positive NOI.Frm (fair market rents) isn't too hard to find, but GRM(gross rent multiplier) is intuitive magic number 10 or less. 

Purchase Price: $100,000.00 Purchase Closing Costs: $2,500.00 Estimated Repairs: $0.00 Total Project Cost: $102,500.00 After Repair Value: $120,000.00 Down Payment: $20,000.00 Loan Amount: $80,000.00 Loan Points: $0.00 Loan Fees: Amortized Over: 30 years Loan Interest Rate: 4.500% Monthly P&I: $405.35 Total Cash NeededBy Borrower: $22,500.00 Monthly Income: $850.00 Monthly Expenses: $840.35 Monthly Cash-flow: $9.65 Pro Forma Cap Rate: 4.15% NOI: $4,980.00 Total Cash Needed: $22,500.00 Cash on Cash ROI: 0.51% Purchase Cap Rate: 4.98% Total operating expenses: $435.00 Mortgage expenses: $405.35 Vacancy: $42.50 Repairs: $42.50 CapEx: $85.00 Insurance: $80.00 Management: $85.00 P&I: $405.35 Property Taxes: $100.00 Financial Info Income-Expense Ratio (2% Rule): 0.83% Total Initial Equity: $40,000.00 Gross Rent Multiplier: 9.80 Debt Coverage Ratio: 1.02

Multiply that by .45 = $900.