And once the network is complete, we do corridors. This is straigtforward geometry: extrude two lines at either end of our connecting line, perpendicular to said line, then join them up. When you do that you get this:
A floorplan which should extrude nicely into the third dimension. However there's one more thing to do before we tackle this, and that is the actual rooms. Which is where things get a tad harder..