There are 2 routes to go as far as getting CAD, or as you say "Floor Plans" software, to run on your Linux box. One route is to run Windows applications in Linux Wine. Not all windows programs work well in Wine but many do just fine. An excellent source of CAD programs for Windows is Amazon. Older CAD programs are very reasonably priced. The other route is to use Linux specific CAD programs. Try this link for Linux CAD programs:
The Open Office suite also has Open Office Draw which is very useful for simple drawings and there are tutorials available to help you along.
Good Luck, Michael