No, it was the former office of IT company Vixitel. Nine reportedly paid $8.25million for it.
I think you have been confused as there were reports that they mocked it up to LOOK like a nine office. I'm guessing the first episode will have the contestants rocking up to what they have been told and think are the Nine offices when in reality it is their block to renovate.
This is what it actually looked like prior to being purchased for the block:
Nine removed the Vixitel logo and out up their own branding in what is presumed to be a joke on the contestants: