Interesting discussion...
The April 7, 1996 Detroit News article about Sunday Drives mentions the mansion as having 42 rooms AND 20 bathrooms.
http://apps.detnews.com/apps/history/index.php?id=98
The June 24, 2000 Detroit News article about Anna Dodge which includes a partial description of the rooms on each floor.
http://apps.detnews.com/apps/history/index.php?id=97
The article mentioned previously about Horace Dodge' purchase of Catherine the Great's five strand pearl necklace for $825,000 also mentions that the 2nd Rose Terrace had 50,000 square feet [[the 1st was torn down to make way for the 2nd one). That size would put it about 11th on Wikipedia's list of largest historic homes in America if it had not been demolished.