First step:We used a laser level with an adapter to shoot the laser as a horizontal line. Then just follow the lines with the tape. Hallway door and closet on the left.
Greyson is happy with his room so far.
After the horizontal lines were done we "simply" added the vertical lines! The large un-taped space will be an evening view out a magic window showing Hogwarts.
Closet and attic entrance. Someday I'd like to do something with that.