A player home must contain at least the following things:
You can then choose the area lightning and ambient music that you want, add placeables, sounds, more doors, waypoints, triggers, visual effects and more!
Each area can have up to 500 objects and 125 of them can be dynamic, a dynamic object is either a non-static placeable, a door, a trigger or a visual effect.
(You may not put in your own items or creatures, or any merchants or scripts beyond those supported on Sinfar's houses script list page.)
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: Players Houses Scripts