You can give it a go but if I was selling I would tell you where to get off.
If the valuer has come up with the same value as you have offerred then I assume he has taken into account all the problems you have found in the Homebuyers report. If he hasn't mentioned them then you need to get back onto him/her.
If the rebulding cost is 28,000 then it is low!!! However if it is 280,000 then it could be right as the land with no house on it would have a value.Depends on the gae and contruction of the property.