Regarding floorplans .... You might try taking a more unorthodox route. Why not try game editors?
Starcraft has a map editor that lets you use an industrial-ish tileset, and is really more of a paint program than a CAD program. Still, it could be GREAT for sketching out things on the fly.
Dungeon Siege has an editor -- props to anyone that can do ANYTHING in it, as I could not.

WAY too detail-oriented.
There might be a map editor for the X-Com games (danged if I know, but if there were, that might be my toy of choice - they have great mundane urban settings.

) With some cheats (or simply going nuts with selling laser rifles

) you could also jsut usethe in-game base editor, or something ... but that's really kinda limited.
I'd love a tile-based editor where I could basically say, "board room here, hallway here, bathrooms here ... research lab and secure containment area over here ...". Ideally, I'd write it my damn self, but I'm too lazy...
I think there's a level editor available for some of the newer games, too -- I think Unreal engine base ones especially... I don't know a thing about these, but you might consider them. They're probably quite capable as a CAD thing, and yet also help you to design areas that are intended to be traversed by groups of humans.
You could also simply sketch it on a piece of paper, and then scan it.

Heck, Paint Shop Pro or Photoshop could do in a pinch. (Though a vector art tool would be more useful, I suspect.)
[edit]
There DOES appear to be an X-Com map editor! yay!
DaiShiva's editor:
http://www.daishiva.com/programs.shtml and
http://www.daishiva.com/programs2.shtml
(The first page is just a reminder that you need the .NET framework. Ack, thppbt! But, still, hooray for hte editor's existence
)
Examples of maps can be found on the xcomufo forums:
http://www.xcomufo.com/forums/index.php?showtopic=3294
I might take the time to fool around with this sometime later today and try to make some facility-ish things. Xcom has some nice warehouses, bunches of boxes (a staple of every game), doors that open and close, heck, they even have gas stations (that can explode)! The maps seem to be largely tile-based (so that the in-game random map generator can build believable things), but I bet you could put together a pretty kickass facility anyways.
Oh, X-Com, I love you so ... now if only the combat used Shadowrun mechanics, I'd be in heaven! (well, not really ... but I do wish it were so
)
[/edit][edit=2]
Apparently, you need to actually have a copy of XCOM:UFO Defense or one of the related games to run this editor. *kicks wall* So much for playing wih this at work. Good news is, Xcom is about $10, and is a kickass game in its own right (albeit the very epitome of old-school).
[/edit]