that sounds like a load of B.S. to me. As far as the roof goes, they should be able to just check the roof from a ladder at several points and get a idea. The roof I wouldn't worry about to much as if it is a new house you should have plenty of warranty against roof leaks on a new home.
The attic is another story. If they are doing crappy ductwork, wiring, etc it is essential for an ispector to be able to get a look at all that stuff.
One thing, a house inspector is on the job, and knows they are in a "construction" environment. For the builder to have any liability there would have to be negligence on their part/ If the inspector were to just fall off the roof due to his own issues, it would fall under his workers comp/disability coverage. The only way being he is on the clock that the builder would be liable would be something like:
some roof tiles are not attached properly and therefore when he "walks" the roof, some tiles slip causing him to fall.
He is walking around in the attic and a joist is not properly installed causing him and/or the ceiling below to fall through.
There is no legitimate reason for them to not allow a thorough home inspection unless they do not trust their own work. That would give me pause about the builder. Personally, I would not give in on this.
