Ohhh, good question! I think they'd get their own, a new home they can make theirs together from scratch. It should be a perfect balance between chaos and order that fits both their needs, and possibly with lots of space for pets.

Law can have his library-studio, and Luffy can have his gaming room, but the shared spaces have a bit of each other in them and you can tell upon entering. You'd think their decoration styles are incompatible, but it's surprising how harmonic it all feels, like further proof of the way they perfectly complement each other.