Roof costs say $8000 (depending on size, shape, type of shingles, etc.) and last 25 years (depending on weather, type of shingles, slope, etc.) ... that's $27/mo you need to put away in CapEx to eventually replace the roof ... now do that for all the systems in the property, add them all up, add some reasonable amount of margin, and you have a reasonable grass roots estimate of what your CapEx should be ... code it into excel with the approriate parameters such as square footage, number of water heaters, etc. and you can knock out a CapEx estimate for a specific property in a matter of minutes, without messing around with bogus rules of thumb like 50% rule or 10% of gross rent, or any other such thing that tries to relate things that are completely unrelated in order to shortcut around actual thought and analysis.Any calculator that you do not understand all of the inputs, outputs and assumptions that went into them are less than useless, and BPs are no exception ... therefore the best ones will be the ones you build yourself from the ground up and modify over time as you gain experience and find that some of your assumptions, inputs, and formulas need tweaking.  

I worked to 70k from 80k because of old wiring and shingle issues. 

It is my understanding when the roofer removes shingles, roofing felt and the substrate.

I always want to do things right , however I don't want install the Cadillac of roofs for $400+/SQ, because I am getting lifetime shingles, ice and water over the whole thing, and other ad-ons.

I'm not pulling up all the OSB and rafters, just replacing the shingles and underlayment and replacing any rotting areas.

Whenever a cloud passes overhead in my neighborhood, the "storm chasers" aka roofers start ringing the doorbell saying hail was in the area and they can likely get me approved for a new asphalt-shingle roof and siding.

What kind of shingles does it have and how old etc. 

Roof in Florida shingle about every 15 years, a/c (10 years), hot water heater (8 years), appliances 10 years, electrical panels (20 years), Take the cost to replace this item and divide it by how many years remaining until you have to replace.. add them all up and you will get the amount you need every month to ensure you have everything covered.  

Lending home charges 150 bucks but they are for real  and can be verified.. all others I deal with over the years and myself included.. no up front fees and no hanging our shingle on facebook.. it cracks me up .. they run ads like this.loans from  10k to 20 million...

Here are a few things that will give you a very good idea of how well it's been maintained and updated working from the outside in:Roof - if you have architectural or composition shingles it will likely be more updated then a house with 3 tab shingles.