Google Draw (?) is a free auto CAD program.
I have a copy of Microstation 95, but it would "against the law" if i was to mail it to you.... you load it on your machine, then you send it back to me.
You might find a copy on ebay. It's a fairly easy program to use.
I bought a garage kit from Sutherlands years ago. I ended up recreating their shitty plans. Planned to see if they might buy them from me.
I do some auto CAD also, but sounds like Colin might be your man.
Don't forget the Floor Dains!!!