According to Ian McKellen:
THE HOBBIT's, two films, start shooting in New Zealand in July. Filming will take over a year. Casting in Los Angeles, New York City and London has started. The script too proceeds. The first draft is crammed with old and new friends, again on a quest in Middle Earth.There is lots of speculation about casting but McKellen will definitely be back as Gandalf.
TheOneRing.net has pictures of the Hobbiton set. The comparable set for LOTR was built well before the filming so the vegetation would have time to grow and would look natural.
Ian McKellen Cinema 2010s