I actually saw a commercial on TV for this a while back:
http://www.punchsoftware.com/products/mac_pro.htm
Shocked to learn it had a Mac version, since a lot of this stuff doesn't. And I actually saw it in my local Office Depot two weekends ago.
Seems pricey, but it seems to have modest system requirements and looks like it does quite a bit. I guess if you were going to be doing this sort of thing, it might be worth that $250 outlay?
But it might be a little more 3D/full-featured (and expensive) than you need?
For my most recent three home re-do projects, I did it all myself, in terms of layout/planning. I used Adobe Illustrator, took accurate measurements, drew everything to scale and used that as a guide. I did floorplans, elevations and angled/isometric drawings. Probably took longer, but I wasn't looking to shell out money for software, or deal with a "new application learning curve", so I just used what I knew (worked on it a few hours each evening for about a week).
Surely there's a cheap, floorplan-only type of OS X product out there...