I am trying to create a room using blender.  

I am following this tutorial:  

<https://www.youtube.com/watch?v=Or9bMxAuICc>  

I am trying to make this image:  

<https://www.artstation.com/artwork/AdEr5>

Ok, so to make windows, i try the boolean modifier.i add a cube, place it in the place of window. i add a boolean modifier to the walls of the room.Then,I set the operation to difference and selected the cube. Next the cube starts clipping.
like this:
[![Inside room](https://i.stack.imgur.com/eD96c.png)](https://i.stack.imgur.com/eD96c.png)

I moved the cube to another layer but it seemed that it did not go:
[![Without cube room](https://i.stack.imgur.com/37c6u.png)](https://i.stack.imgur.com/37c6u.png)

although the cube was on another layer:
[![Cube on other layer](https://i.stack.imgur.com/tnlZR.png)](https://i.stack.imgur.com/tnlZR.png)

I went out of the room and there i found a hole but it wasn't cutting through the wall (P.S. I do not have a solidify modifier on the room)  

It was like this:
[![hole in the wall](https://i.stack.imgur.com/qmEPb.png)](https://i.stack.imgur.com/qmEPb.png)
I investigated more and i found that the cuefdged theroomwith I really don"t know how to say it but here it is:
[![Cube with the wire](https://i.stack.imgur.com/wRtjt.png)](https://i.stack.imgur.com/wRtjt.png)

I have tried everything with the normals. Flipped them inside as well as outside. Recalculated them. Applied the scale. Nothing works.  

Please help I'm stuck. This has never happened before.  

I am also including the .blend file.