As awesome as it is to have a room, our levels are actually going to be much larger than this. Let's open an opening to the rest of the levels by creating a doorway.
Now, if we had ProBuilder, we could use the subdivide tool and modify the faces to open up a doorway. But in our case, we will rebuild our room, taking the door into consideration:
Let's go ahead and delete our floor/walls object and move our original ceiling back down to
0,0,0.
Let's press Ctrl + K to spawn a new brick and bring it into our scene. Move it so that it snaps to the edge of our room, making sure that the Prototype subselection is turned off before the movement.
In the Prototype tab, switch back to the Element/Geometry mode and select the face nearest to you. Move it so that it is
3units wide, leaving room for our doorway in the center. Hold down Ctrl while you do so for it to be even.
Hold down the Shift key to extrude and pull it forward a bit. Then, hold down Ctrl to start snapping again and...