Builders Level Video
Your project calls for a level line around the entire room. This line would be needed for crown molding or a suspended ceiling. How do you do this? Using a 4 foot level and drawing a line around the room is time consuming and can lead to errors.
A better method is to rent a builder's transit or builder's level. This tool sets up on a tripod and uses bubble levels to get the instrument level in the room. Sighting through the level, mark the wall at the required height. A helper will be required to make the marks. Once the marks are created around the room, use a chalk line to create your line.
These builder's levels are easy to use and can be rented at most tool rental stores.