hiya Flossam,
tbh, the surveyor is probably covering their backside. They need to point out anything that you might find 'down the line' so to speak, so there's nothing easier than saying 'looks like there might be damp' and there are holes in the roof.
Realistically, this house may be empty and unheated, and the last few months have been cold and wet, so that may be contributing to high damp readings. As others have said, to treat it (if it's not v. bad) is fairly simple. I wouldn't worry about this till a proper damp company has looked at it.
Re: roof - tiles slip all the time, and on an old house the roof has probably had piecemeal repairs. The guy probably stuck his head up the loft hatch, caught a few glimpses of sunlight where tiles have slipped or the lining felt has failed etc. and, well, you've seen the report... You might want to have a look yourself to see what you think. Perhaps only one area needs some attention ? A roofer or DIY blokey might remove an area of tiles, refelt and replace in just a few hours... impossible to tell without more investigation.
To summarise, if you've looked long and hard, and this place is at the right price, I'd be wary of chucking it all in until you're more fully informed. Use these 'negatives' to hassle the buyer on price !
But be warned, these old houses do take a lot of money to keep going. There's always something aging / breaking / sagging / failing etc. and it's not always obvious ! Be careful about stretching the finance so far that you can't take care of a boiler that dies or a window frame that had been painted over but is really shagged...
HTH.