Material amounts discovered in due diligence is, in my mind, NOT considered re-trading, nor frowned upon.  

Any body you see buying a lot of flooring material introduce your self in ask if they have a business card.

What are the best tool to estimate a flip materials cost?

I was approached by someone who has the resources (men and material as he was in roofing business) to partner up and buy MFs. 

Property tax % can be quite high in the Austin area and will affect cash flow materially.

I always hired contractors, and did material runs for them several times a week after work and cleaned up jobs on the weekend, which was also time I spent at the properties, discovering issues, thinking about the rehabs and what needed to be done next.

What I have done in the past is that we (myself and the contractor) discuss the project with as much detail as possible, what materials will be needed, how many people will work on the project, how long it will take, when they plan to start and finish, work schedule, and what the budget/price will be. 

All mid level materials for a flip.

When you run a business however, you can write off a lot of materials, equipment, software, etc.. that can help reduce your tax bill.If there is a cheat code to this, I am all ears!! 

The most dangerous kind of aluminum wire was mostly only used for residential wiring from ~’65-‘73 when copper was prohibitively expensive (Al alloys that are less dangerous were used with less frequency post-‘73, and Al is still a common material for transmission and distribution lines, and even some residential use like AC units or single branch circuits, but not very common in residential wiring).