Hi Anis,
Yeah you got it. I just drew single lines representing the walls. Then I extruded them to the height I wanted. Then I chose shell and picked the thickness. It was pretty quik though I looked at it again and noticed some of the walls were not inline. The shelling would have to be done "Wall by Wall" to be able to select the direction of the shell ( the shell commands "normal or flip" option). If doing large buildings this could get time consuming where your original request for a 2 line tool would eliminate the need for these extra steps.

If you want me to illustrate it I can but you can see the 3 steps in the picture. In my corrected file I selected each wall seperatly, shelled it, looked if the direction was proper then either switched it or moved on.