Offline index rebuild - does it also create a whole new copy of the index?
Consider what Paul Randal says in his post on Search Engine Q&amp;A #19: Misconceptions around index rebuilds (allocation, BULK_LOGGED mode, locking):


  Index rebuild (whether online or offline, and at least as far back as 7.0) will create a new copy of the index before dropping the old copy.


He reiterates that point in SQLskills SQL101: REBUILD vs. REORGANIZE:


  Rebuilding an index requires building a new index before dropping the old index...


Finally, the documentation also discusses this on the page Reorganize and rebuild indexes:


  Rebuilding an index drops and re-creates the index.


So the answer to your question is yes, a new index is created and the old one is dropped when rebuilding an index offline (although it will generally require less disk space than the online version of the operation).