Installing a ducted air-conditioning system into a congested tight roof space is not a particularly easy task. Most experienced builders are quite aware that the roof framing including trusses, battens and their connections are not to be damaged or compromised in anyway.
Air-conditioning installing contractors are however not usually licensed builders with a carpentry trade behind them. This can result in a lack of respect for the integrity of the roof framing and damage if modifications are attempted "on the fly" by the air-con installers.