Help! Old roof repair has come back to haunt us!

I am hoping to get some advice regarding an issue we are facing at the moment with our roof.
In 2006, just prior to purchasing our house, we had a building inspection carried out, which revealed some problems with sagging in the roof due to a hip rafter and purlins.
Work was carried out to rectify the issue (organised by the previous owners to comply with our condition of sale), including the installation of a steel beam to support the front hip and purlins. The sag remained but we were assured that the work was completed properly.
Recently, my husband was looking around in the roof and noticed that there were some cracks in the wooden hip rafter and purlins and we asked some builders to come and look at the problem. Both independently said that the initial work was not done adequately to support the roof structure and that is why these problems have occurred.
We managed to find the original paperwork and contacted the original builder. He had a look and claims that the problem with the cracking is unrelated to the work he did, which is contradictory to the advice from the other 2 builders that came to look.
We asked to see the permit and engineer report from the original work and he said he didn't have one as the work was done under $3,000 as it was a "job for a friend". Our understanding is that is is structural and therefore should have had a permit. The quote to have the work fixed is $15,000 - a huge difference from the $2,508 that it originally cost.
Hopefully someone here has some advice or recommendations for us. This is all foreign territory to us and don't know what to do. Thanks for reading!

Sounds to me you’re going to have to wear it unfortunately. 14 years ago would be the time to ask for engineering plans and permits.
Could you try your home insurance? May be a long shot but it can’t hurt to try.