To those whove had experience, how would you create buildings in ue4?

So i’m having trouble with creating buildings and rooms and all that, so i wanna ask to those who’ve had experience making buildings in ue4. To those who’ve had experiences making buildings and interiors, i ask how do you do it? do you make the whole building interiors and all in your 3d modeling software, and then import it and add collision, or do you make pieces of the building and then put them together in ue4?

I am working on a low poly game so I make most my models in engine and I create modular pieces when possible to speed up development.