For me, I don't want the estimated repairs to be more than the price I pay for a property. There's always something more than the best "swag" can predict, and that's getting a little risky for me. As for caved in floors, you've got to get the story. Why did they cave in, refrig leak, washer, interior plumbing, roof, dry rot or what? Estimate to repair the cause and the result.
I use xactimate. It has a feature that will actually rebuild structure, floor, walls, ceiling or rafters by plugging in the size and centers of joists, subfloor etc in 3-D and price it out. You've got to add in a little more for spiders and snakes. If it was due to long term water damage, you may have to install a few new piers and deal with mold.
Like I said there is always something more, but this is what I would look at.
