Just start asking questions, someone will have the answer.
Did your son check the roof? That's probably a good place to start. There is no point restoring the inside until the leaks are stopped and any water damage is repaired.
The roof may need replaced.
Tires? They probably need replaced.
Has the rig been sitting? Belts and hoses may need replaced plus, all the fluids. Brakes?
I would tell him to make a list of what needs replaced and check prices before spending any money.
A free motorhome can get very expensive very quickly.
There's probably a reason it was given to him.
That said, I hope he can get it restored and useable. The older rigs are cool looking have class.
It probably will not be cheap to get it back on the road.
