How do you get estimates from contractors?

[Yusuf Qureshi]

I am reading the BRRRR book, and I was wondering how do you get estimates from contractors for rehab projects?

The book provides a format activity/scope/price. Do you use something similar? 

My contractor just gives me an estimate without much detail. Should I ask for more detail: Scope/Activity/Price? I do not want to add any unnecessary work to my contractor, however, I want clear expectations to avoid any confusion. 

Any articles/books recommendation would be great. I want to understand how contractors operate to make sure I understand their business need.