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The interior of you house can be built using the Neverwinter Nights Toolset.
There's a few restrictions, they can be found on the page where you can upload your areas once they are done: https://nwn.sinfar.net/houses
Here's what the process looks like:
The housing system is made so that you can even make your own scripts for inside your house and they will have no effect outside of it when ran. This feature is although restricted to selected players and Sinfar Supporters.
Read more here: scripts