Who is responsible for coordinating roof system accessories to make sure everything works correctly?

Who is responsible for coordinating roof system accessories to make sure everything works correctly?

According to AEP Span: 

It is always recommended that you follow the installation instructions of the accessory manufacturer.  The installation directions must be followed correctly to prevent any unnecessary damage. Damage caused by installing an accessory incorrectly will not be covered under the roofing manufacturer’s warranty.  To review AEP Span’s warranties, visit ourWarranties Webpage.