How do you unlock the third floor in super Mario 64 ds?

First, you have to unlock the basement by completing 'Bowser in the Dark World' (get 12 stars first). Then, in the basement, you have to unlock the second floor by getting 30 stars and completing 'Bowser in the Fire Sea'. Then, to unlock the top floor, obtain 50 stars and go up the set of stairs on the second floor. Go through the door and you are now on the top floor. (Get 70 stars to get up the endless stairs to 'Bowser in the Sky', complete the level and you have won the game). Result!