Two feet! WOW!!!
That is pretty good size. I am not certain of the different sizes, but I do know that there are a variety of Star Destroyers in the RESOURCE Section.
If nothing else, yo could look at scratch building one as well.
I knew there was a nig one in there. If you have Photoshop, you can make it even bigger. You just have to break down the parts more. Sometimes, that adds some realism too though.