There's a beautiful slideshow of movie sets from Architectural Digest, including the redesign of the Great Hall to include the Knight Protectors, and the new location where poor Snape will meet his demise.
Spoilers!!!
Architectural Digest: Inside HP and the Deathly Hallows with Set Designer Stuart Craig "Part of the Battle of Hogwarts takes place in the school’s entrance hall, which was redesigned
for the scene. “This is one example of how things just evolve and how Hogwarts changes from one movie
to the next,” says Craig. “In the final battle, it’s required that the statues jump down and take part in the battle.
So we needed to change the look of the entrance hall.”
"The boathouse at Hogwarts, described by author J. K. Rowling as an underground harbor, was designed
as a light-filled building for the film. Featuring Gothic influences, the set is the site
of a dramatic meeting between Voldemort and Severus Snape."