Ok Jojo I have no idea myself and it appears The Builder is not around. Can I suggest you get a builder to have a look, preferably one recommended to you, and they should be able to give you an idea of the cost. You will then have a figure to take back to the estate agents and do some negotiating if you still want to proceed, although some allowance for these works should have been made.
Another point, how long has it been on the market? Also, have you checked the price of similar houses in the area? One last point, if you are getting a mortgage, was the report on behalf of your mortgage application and if so has the bank agreed to lend you what you asked for having seen the Surveyor's Report? If they have, then they must be happy, unless of course you have put a large deposit down hence they have nothing to lose.
Sorry, more questions than answers? Q a song;-))