Who set the Weasley's house on fire in Harry Potter and the Half-Blood Prince?

Answer 1

Well Hogwarts doesn't really burn down in any canon of Harry Potter. In the book, the battle is concentrated in the Great Hall and in the Great Hall Antechamber, so that's the only real place of total destruction. In the movie, however, the castle endures the destruction of buildings, bridges, and the Great Hall is yet again a great zone of battle (although the Viaduct Courtyard sustained worse damage and had more deaths per person than perhaps anywhere else in the castle. The castle didn't actually burn down. If you referred to the poster, that was to attract attention to the movie. The film had alot more death and destruction though.

Hope this kind of settles your question.

Answer 2

Bellatrix Lestrange with the aid of Fenrir Greyback. This scene does not happen in the book only the film.

Answer 3

Nobody, in the book Hogwarts is still standing - however badly damaged.

Posters for the film however, appear to show Hogwarts on fire. It is unknown who or what caused this.

Answer 4

It was never specified exactly who rebuilt Hogwarts, it's only known that they must have been wizards as muggles cannot see or know about Hogwarts.