The low supply of them, combined with high demand make this one of the most competitive asset classes in an already competitive market. 

When I buy multiple things on a reciept I don't know how to entet different amounts into what category.example: Buy paint, a tool, and all the supplies to put on a roof on the same reciept.I assume all the material for the roof goes together but in what category?

The BP calculator does not know unique location dynamics, supply and demand, redevelopment, gentrification, demographic patterns, job and population growth or lack of, schools, crime...you get the picture.

., go to the local supply shop (not the big box places, but the places where the pros buy supplies). 

However, the lien dissolves unless the party claiming the lien files a certificate of lien with the registry of deeds of the county in which the property sits within 90 days of the last supply of labor or materials."

Turning the water supply off and draining the lines reduces the risk even more.

However; there's no guarantee of what the market in the future will do, as every area is different and it depends on supply and demand at the time. 

I went to home depot got day laborers ... bleach and other cleaning supplies all done for a few hundred.

The supply lines get blown out , hot water heater gets drained .  

And employment reference should be similar - any phone number the applicant supplies might be a friend who was asked to pose as the reference.Why?