ythread wrote:

I'd go check with the local code officials and see what the code
says. In most places you are permitted to have 2 layers, but no
more. Also, in most places you need a building permit to put on new
shingles. Find out if one was taken out. If the answers to both of
those questions are no, then depending on the rest of the facts, like
the age of the roof, I'd seriously consider going after the seller ad
you could have a slam dunk case.

Why would the seller know anything about roofing?

Unless someone snunk over and re-shingled his house in the dead of night,
the seller knew there were three layers.

Three layers is certainly something noteworthy and maybe illegal.

On the other hand, maybe it's the third layer that's holding the house
together.