The big repairs are mostly plumbing, electrical, HVAC, roof and siding. Paint can be expensive too, depending upon what is needed. I just walk into most deals with the mindset that 3 or 4 of those items will have to be done and so it's priced in.
I just price in what I THINK might need to be done and add 30% to that figure.
For instance, I just bought and rehabbed a house with an ARV in the low $100s. I paid about $35,000 for it.
Well, I just priced about $25k in repairs and that was putting me at about $62,000 with closing costs. Still a pretty good deal on a house that I could easily rent for $1000 per month.
Turns out, the repairs came in at about $13000. So I am in it for $51000.
People try to be too analytical. When you are buying homes for WAY less than replacement cost, there are not too many ways to lose money, so I'm not much on contingencies. In fact, I have never backed out a of a wholesale deal once it was under contract, and I have yet to lose any money.
And I don't sell to buyers who want any contigencies either.
Like Larry Goins says, "If you need a calculator to think the deal through, then it's not a DEAL."
I swear, if a person cannot make money in this real estate market, they absolutely need to be doing something else. It doesn't get much easier.