Although I placed a 30 FT antenna on my roof top and I have one of the tallest building in the area, I wasn't able to get my WiFi signal out very far because the trees got in the way.Maybe you can avoid the interference issues I encountered, but how will you compete if Google give out free Wi-Fi?

All new electric, plumbing, subfloors, floors, wall covering, roof...everything!

My first rental has a roof leak , my regular roofer is on vacation for a month .

She did not know the age of the roof.

And by the time from the house being under initial contract all the way to finally selling the thing.... months of time and hassle, although costs should be accounted for its still allot of unnecessary risk and time spent with a house on your mind for not much reward. instead of using a 70% rule, do a detailed estimate on the big array of holding costs associated with inquiring and holding and selling a property, that will give you an idea of what would be reasonable for a cash buyer to need as motivation to pull the trigger.

I have a property identified for potential purchase. 1920 2bed/1bath new roof,  pipes,  water heater. 

The 10% is good for regular maintenance but when the roof, the HVAC or the plumbing goes you had better have some capital reserves.

@Bob Bowling, how would you describe your tone in the following post?

Just always ensure the property fits your strategy and meets your standard baseline criteria (roof, mechanicals, bones, neighborhood, interior, rental market of area, and desired CAP.) 

You're going to want to look at the expected life on the major systems...plumbing, electrical, HVAC, roof, etc.