new roof issue came up, need some advise with it

[Dmytro Sulyma]

Hi everyone, just need someones advise what to do here... Me and my wife bought a house one year ago with a brand new roof. We transferred warranty and got all of the documents in our name. So another day i found that the new plywood in attic has a lot of mold on it. A lot of nails are rusted and some has a little bit of water on. We called the roofing company(who installed it) and they were able to check it withing an hour. The guy said that the reason of mold is that there is not enough insulation. I have very little knowledge about roofing but i believe that its also ventilation problem, as the damage is pretty serious within just 1 year. My question is 1. is roofer required to install a proper amount of insulation? 2. does roofer required to provide the right amount of the ventilation? 3. if you could recommend me what could i do in this case?

just my add to the story, when we bought a house(wa state) the brand new roof was a big deal for us and we were super happy to dont worry about it for at least 10-15 years and now we dont know what to do because even after spraying the mold you still gonna be able to see the stains on and it will come up on a inspection when we try to sell the house. Its a real awful feeling to have a new roof messed up within a year. THANK YOU FOR YOUR HELP.