Sorry, I don't have a Mac so I don't know what's out there for it.
However, someone else here (can't remember who) posted a floorplan that he made using http://www.floorplanner.com
and it looked very nice. As far as I know it's free for personal use, and may work for you if you want to check it out.
I prefer Home Plan Pro above the others I have and use, but sadly they don't offer a Mac version at present.
Here are some possibilities you could check out from download.com (I find all kinds of useful apps there) : http://download.cnet.com/1770-20_4-0...platform%3DMac
Wish I could be more help.