Wondering what kind of form/estimate sheet you all give your contractor?

I've completed various renos, usually on the smaller side <40k and always used an excel spreadsheet with what is to be done, kind of broken down into categories - flooring, roofing, painting etc. Never done a full house flip however. 

For each category I have a price/estimate - then essentially compile everything to get to my estimate. I've typically found the subs I want to do individually - however I this next one I'm using a contractor. He's a small company and does a lot of the work himself, so he doesn't charge the 20-30% on top like most of them do. Found him through my property management company (he's one of the guys they use). I have also generally used verbal estimates (I know there is a better way to do this) and I give an amount to NOT go over. If this is to be exceeded, then I need to know why and about every cost from here on out. 

The other thing is payment - I NEVER pay for jobs up front. I will pay for materials and ask for receipts. I typically will split the jobs up into 3rds or 4ths and pay in sections of work completed. I do get a 1099 from from them to so I can add whatever the amount is into my cost basis and depreciate it. 

I was just trying to figure out what the "standard" was, for what you all do for larger renos and flips. There's a lot to keep track of and a lot that can fall through the cracks. And there's always the estimate vs the real cost.

Any advice to standardize and systemize this?!