500 quid if you dress up as Laura Croft and do it ,550 if you do one of those handstandy things on the edge of the roof.
Seriously though , its a dumb fucking idea.
Truly .
Forgetting about the fact that you'll probably break your neck/get suspended/expelled.
Dressing up in a cloak and hood and prancing around ontop of a building in the US? you'll probably be mistaken for one of those 'mustache-men-land' terrrrrrists and shot in the face repeatedly by some patriotic cop.
Lastly the only way to recount a story of such stupid bet related daring is "well we were very drunk and it seemed like a good idea to..." , "I spend 10 and a half months preparing to..." just doesn't cut it.
TO sum up:
Bad idea , bad.