When this rent is subtracted from the gross income I have a hard time finding properties that work out to cover expenses and mortgage.

Take your estimated rent and subtract vacancy, management, insurance, property taxes, maintenance, repairs, and cap ex. 

Conversely, after each week the contractor is behind schedule, tell them you will be subtracting 4-5% from their quoted price.  

To give you some sort of an idea is that 75% of the Value is a good place to start.So, if your value is $300k, then 75% of that = $225,000 <-- This represents the COMBINED Loan to Value maximum.We would then subtract out your current mortgage from that maximum...$225,000 - $175,000 = $50,000  <-- This represents the amount of a 2nd lien you would get. 

I'm working on a master investor policy that you can add and subtract properties on and pay a daily rate. 

You shouldn't live and die by those rules, if I were you I'd just subtract the repair costs from the asking price and maybe take 5 or 10k to start. 

Formula : Potential Property Sqft X Average $ for sqft ex) 1,500 Sqft X $75 (avg) =  $112,500From here I would subtract the repair and aquisition costs, and if i'm buying from a wholeseller I would subtract thier costs. 

For example (with made up numbers), the Brevard County FL office where I have section 8 rentals takes the fair market rent (FMR) of $1000, subtracts utilities allowance (UA) $200 and they post a spreadsheet saying for zip code XXXXX 2 bedroom house I can rent it for $800 if I’m requiring the tenant to pay utilities.

You are making 40% gross return.To calculate net, just subtract your expenses.

To follow up on what Amir said, to find the NOI a great strategy is to subtract your expenses from your gross operating income.