I want to share my method to draw precisely.
I use it mainly for existing buildings where surrounding rooms with walls are not an option wile walls could have different thickness.


Set the precise dimensions




Zoom in and mouve walls in precise position





I use Advanced Editing plugin.
Note 1: For high accuracy use high zoom
Note 2: The accuracy is at least 1mm with this program which is enough for any one who want to build a house and not a space shuttle.