Once we defined each area with walls and the surface tool, the room square footage appeared in each space. It is easier to see the text box if you turn the Floor Visibility up. You may also want to turn up the opacity of the original sketch so you can see the room names and dimensions, or work from a printed copy. If you turn up the opacity, turn down the Floor Visibility a little to see through to the original sketch.
You can move the text box around to make it easier to work with.
In the Room box that opened to the right, type in the room name in the first box and the room dimensions in the second. Change the font size by clicking on the icon with the 3 dots to the right of the room name box.