What is the best way to create buildings?

I use Blender for modeling.
I created some small Props, Weapons, Trees with Blender since I started with it.
Soo, I’m not sure how I can make a building without spending to much time on it.
Should I make something like a modular system? Or the whole house and then export it to UE4?

make modular pieces. look for good examples on the marketplace for such.