How do you estimate repair costs?

[Owen Thornton]

Hi. I was curious how you go about estimating repair costs.

I have gotten pretty good at analyzing deals themselves and figuring out what purchase price/LTV will help optimize returns... but in such videos as Brandon Turners ( attached below video)

..

I tend to struggle to figure out where you exactly get the figures for a rough repair estimate without a contractor inspecting the property. 

I understand it comes with experience, though is there any general rule you should follow?