There are a couple of PA's that make rooms that are designed to fit together. I'm thinking specifically of the Tesla3DCorps products, like this one:
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There are a few other rooms that go along with that set/theme.
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Anyways, it's also possible to graft rooms together, but at this point you are sort of building your own house. It might be easier to just use cube primitives for your walls and floors, using texture shaders or copying textures from existing rooms if you are grafting things together.
I ended up spending a lot of time building a house grafting the above linked products to other existing products, as I needed to use a couple of specific rooms for fanart as a 'homage' to the source material. It ended up looking like this:
I had to build the entry hallway mostly from scratch, along with the stairs to the second level. Anyways, my point is that you can graft stuff together, adding additional hallways/stairs/rooms as needed, and make it look nice, it'll just take a bit of work. At that point, it might be easier to just build your own though. The nice thing about existing rooms is that they come with shelves, doors, wall outlets and such.
There are a few 'complete' products out there as well. I'm specifically thinking of TruForm's stuff, such as this one:
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There are other vendors that have a few 'complete' houses as well. And then there's always the extra knick knacks that you may decide to add to the various rooms...
Anyways, it all comes down to how creative you are and how much time you want to spend putting a house together.