We don't have much money, but at least we 'have a roof over our heads'. [=at least we have somewhere to live]
You'll do what I say as long as you're living 'under my roof'. [=as long as you are living in my house]
We hope to have sales and service 'under one roof' [=at the same location] in the near future.
(..) WOMAN: That's enough, kids. Say bye-bye. Listen, I'm gonna send some presents with Grandpa, all right? And you be good, you be... - Our ride's on the roof. - Right. Hey, are you okay? Yeah. Yeah, I'm fine. Why? Well, down in the dream, Mal showing up. (..)2010 Inception