I posted this idea in another thread, but that thread seems to have got lost somewhere.

Anyways, my idea would be after a hut is built it slowly deteriorates. My reasoning behind this is that once all items are built there is nothing left for the builders to do and no way to make master builders.

I had this one villager, who was one of my favorites since she was a runner, who mastered farming and research and was trying to master building. She never made it past adept before passing away as I hadn't realized that I had everything built for that level and was no where near making it to the next.