Hmm, well I tried it on another computer and it works fine (almost). The only problem seems to be the "Join walls" does not join the nearest points on the selected walls. Instead it joins (I think) the endpoint of 1st wall to starting point of 2nd wall.

Also, it would be nice if input dimensions could be in feet too. And have "relative dimensions" in "Edit Points" dialogue.

All in all, a wonderful start though! I'd been hoping for some precision features like this for some time [:p]