表达 “a roof over one’s head” 用 “头上的屋顶” 来比喻一个人的 “栖身之所”，即 “住处，居所”。

例句
Ben’s friend lent him some money so that he could get a roof over his head.
本的朋友借了他一些钱，他才能有个地方住。

My parents always remind me that they give me a roof over my head and that I need to live by their rules.
我父母总是提醒我说，既然住在他们提供的住所中，我就要按照他们的规矩生活。

I just need a roof over my head for a few days until I get paid.
我只需要在拿到工资前找个地方暂住几天。