Man on roof

Our mate Kev came to fix the gazebo today. Guess what.... It was leaking!!! That's what I suspected but the man that built it said it 100% wasn't and said he would come and see what was happening. That was 4th December. Not heard from him since.

Kev went and bought more supplies to put a tilt on the roof and replaced the felt.

How do you go about claiming money back from a tradesman and is that even a thing?