Basically you will see the ceiling /roof of your house as if it were the floor.
A door will apear to be a windows and when you walk through it you get the feeling you crossed a concrete base of a windows.
Also if the roof has two different heights crossing from one area to the other with the other roof will spears as if you walking on the air.
Step 1: How to Make It
You only need a retangular mirror aprox
4" by 6" inches or around 10 by 15 cm
Place it just below your nose
Now looking to the floor will actually show the roof since the mirror is on the path your eyes use to look to the floor
Now you will walk but the images to guide you are all non real since you actually seing the roof.
Step 2: Discussion
Ideally the floor should be a totally flat surface with smooth finish and without any obstacle such as table or chairs or any other regular house furniture so that you know you can walk without knocking on something the mirror is blocking you from seing.
Also ideally the roof should have two different levels or other similar irregularities since this will appear to you to be a place where if you walk you will fall.
In any case I just tried that with my daughter and we obviouslly did not have a special floor (with no obstacles) or a special roof.
Even so we had a lot of fun.
The picture I took from her was on the
terrace and we live in the eight floor of a bulging with a little terrace.
Walking into the terrace would appears to us that we will walk in the sky since the roof of the terrace is just the sky above the building.
The sensation of walking past the visible floor to the sky is amazing.
Also the chandeliers (house lights) would appear as obstacles and you can just pass through them as if they were non material.
A regular door would show up as a window with a concrete wall just in front of your feet and yet you pass through it
If you try it post a comment here :-)