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.
(..) I don't feel the least bit bad about it. What the fuck I tell ya, huh? As soon as the word got out the fix was in, man... the odds went through the roof. I know. I know. Unbelievable. Hey, fuck him, Scotty. If he was a better boxer, he'd still be alive. (..)1994 Pulp Fiction