It has no roof? I didn't see one in the video but I figured it must have. I haven't tried this but if you
have Dialog System this might work
Add a cube just inside the door.
Disable or remove the renderer component, and tick IsTrigger on the BoxCollider.
Add a Sequence Trigger.
Set the Trigger to OnTriggerEnter.
Set the Sequence to SetEnabled(MeshRenderer, false, Roof)
where Roof is the name of the GameObject with the mesh renderer.
Repeat steps 1-3 for a cube just outside the door, but change the sequence to:
SetEnabled(MeshRenderer, true, Roof)
When the player enters the trigger just inside the doorway, it will disable the renderer. When the player steps outside, it will re-enable the renderer.
Probably a blox or 2 could also do this?