Nick,

This could be easier than you expected. I did something similar in 2007. If
the Lords at Autodesk have not changed things too much, it'll still work.
Essentially you're asking for all floor polygons to be exported to CAD. So
if that's AutoCAD, then create a text file, rename it as filename.scr
(script). Paste the polygon block from inp into this scr. Make edits so
each polygon vertices are arranged like this:

Line $ cad command
x1,y1
x2,y2
x3,y3
$...so on. No need to repeat first vertex.
Close $ cad command

A bit of simple VBA will save precious minutes and provide happiness like
no other. Simply dragging this scr into an AutoCAD drawing should do it.
You may get rid of overlapping lines with the rightfully called OVERKILL
command.

Note: For several shells, do this with separate files and put contents into
separate layers each time you import. Or, for geek satisfaction, check the
command sequence AutoCAD uses when you change an object's layer. Enter
those commands in your scr at appropriate junctures, and expect everything
to behave.

Hope this works. If not, oh well...was a good story.

Good luck,
CJ