You can use Place Doubleline Command 
to place a doubleline as you draw and clean corners as you place the lines. This
command is very useful in drawing an architectural floor plan for a house or a factory.
Place Doubleline also miters joints and trims as it you draw. It puts endcaps on single lines.
On the Place Doubleline Ribbon, you can define the thickness of the doubleline and whether you draw the doubleline from the left, right, or center.