1 Wall and a floor

Hello. How to create only 1 wall and a floor? Or 2 walls and a floor? 

If i choose - CREATE ROOM - Draw - By EDGE or By center i can design a wall but than no floor. 

If i click EDIT FLOOR the system show's and info: 

"Please Draw a room first"

But i want to draw a room like a  fair stand exhibit, i dont need walls. Just one in this case. 

How to draw 1 wall and than draw a floor ? 

Thank you