MRUK Create a new Scene

Note: I am an Unreal developer, so I apologize if any of this is slightly different to Unity.

You do not create rooms with MRUK, rather MRUK helps get access to rooms that are saved on your headset via the Space Setup app (Settings -> Physical Space -> Space Setup).  Setting up the room includes scanning the room to create a 3D mesh representation as well as adjusting planes and adding volumes to represent semantically labelled objects, like walls, floor, tables, etc.  This is a completely separate process from your app and can be done prior to running your app.  If your app finds no saved room during runtime (i.e. Load Scene fails), you can launch the Space Setup app from inside your app, complete the process, and it will return control to your app, at which time you can use MRUK to access the data.

MRUK also has helper functions to convert a loaded Scene (i.e. room) to a JSON string and load the JSON back again into a Scene, as if it came from the headset.  This can be useful for debugging or learning, and the MRUtilityKitSample project has examples of this.  I highly recommend checking out the sample, as it also shows how to request the necessary user permissions to access the Scene data.

Once your app has received permission and loaded the Scene from the device, you can do something like MRUKSubsystem.GetCurrentRoom.IsPositionInRoom() to check if a position is inside the walls/floor/ceiling volume.