Secure the flooring since any leaks could cause subfloor damage under a toilet. 

However lack of communications from your GC / builder I agree frustrating and can be a killer to the GC's reputation..

Look for signs of water damage, like stains or discoloration on walls.Roof problems are also common.

Possible his drone showed the most evident damage and not so much like being on the roof.

But if you are able to risk the money without damaging yourself financially and it's truly your passion, then sure. 

My reputation hinges on it, and with that my income.

Last year, a heavy rain and storm damaged it and I had to replace the entire roof which costed me $21K. 

., major structural termite damage, small mold issue).

I have worked on hundreds of REOs and have done a few for smaller reputable groups that heard my name because of my reputation.

If the later is the case, unless your contract with that buyer had specific performance language in it, there is nothing you can do.As to the advice above about potentially clouding title, you are now entering the legal realm and you should NOT be taking legal advice from anyone other than your attorney as clouding title in THIS case can swing back at you from the original sellers for not performing and claiming damages against you.If you intend to wholesale, you need to do it legally and ethically and in many states, that requires either a license, closing on it with your funds or borrowed funds, then marketing for resale once you have title, or having your buyer upfront, forming a legal entity with both you and buyer as owners.