Close lines help

Trying draw simple floor plan.

Using Polyline and offset to create walls.

How do I close the open end of the poyline and the offset line?

Thanks for the help

There is no automatic tool for this. Just draw a line between the two endpoints. You can the use  Tools - Polyline - Create Polyline from Existing Segments  to make a wall element as one polyline as long as there are no intersecting or forking lines.