Now that Zandronum has officially released 1.0, non-sloped 3d floors become fair game in AOW mapping. Please keep in mind, though, that they tend to be pretty heavy resources-wise so please check the framerates in software! Be cautious in their usage, don't just spam them for the sake of spamming them! "too many 3d floors dropping the framerate" is a perfectly valid reason to reject a map in my books.

Also note that sloped 3d floors are invisible in software, thus their usage is not advised.

And if you're using 3D floors, it'd be a good idea to make them useful (not just for the sake of detail, but for gameplay too), but this is completely up to you. Just an advice, because they are very resource intensive.