The only way it goes back light is if I click on one of the walls and I make it a half wall
What you are seeing is normal. I see the same thing when I use the room tool to make a room or use the wall tool to make a room. The darkness comes from no outside light being in the room as it is fully enclosed by walls, floor and ceiling. There is another thing you can do to lighten a space while you build. Select the room like you have done in your pic. Go up a level and click on the yellow outline and delete the ceiling while you work. When you're done with the room, put the ceiling back. That won't work if you have a room above though.
Hope this helps.
