Most can't quantify the expense in the way that I describe here, but it becomes very obvious over time.  

I generally buy my materials similar to your second scenario, where I buy all the finish materials and the contractor provides all of the 'rough' materials such as plumbing pipe, fittings, wiring, lumber drywall, etc.I try to buy all of my materials in bulk orders...generally two bulk order per project...It depends on the schedule and the scope, but I will generally buy one bulk order upfront to get the project started & a second bulk order to get the project finished...Quantifying materials, and walking around Lowe's seems to take a couple hours for each order, but if you do a lot of rehabs you can create a list of typical SKU #s, which should help shorten the process.Also, if you buy in bulk you can generally send the order to the 'Pro Desk' and get 10% off the order.

It depends on how you're quantifying it -- but in general I'd think everyone's top three would be something like this:1.

I like to tell folks to have some type of goal in mind - in other words - what is it you are looking to achieve through investing - of course the cash flow and appreciation - but quantify that a bit - is this to replace your active income, is this to diversify your portfolio, to hedge against inflation, etc - by having a specific focus it makes it a bit easier to figure out which direction to go, what types of investments to point out to you and get you closer to what it is you are trying to achieve. 

I have been taking martial arts for decades. 3rd degree black belt.First you need to quantify martial arts school.

If it's the first time you are driving for dollars, how did you quantify that 15 properties matched what you are looking for? 

I think the problem with putting a dollar value of the risk of that happening is impossible for someone to quantify.

Nevertheless, it was interesting to quantify this trend for a specific real estate market.I’d like to do more market data analysis, if you have any ideas for interesting metrics or specific RE markets you’d like me to take a look at let me know!

They can't see how much work you did behind the walls with framing, quality insulation, updated electrical, super quality craftsmanship on the plumbing.. it matters that you have updated mechanicals and they will quantify it but... what really matters is the quality if your finishing work. 

I didn't quantify it, but my feeling was that they were a lot more likely to cancel showings than others.