Tomahawk Kill on COD Black ops Nuke town?

Okay so my friends were showing me this planned tomahawk kill in nuke town. Someone stands on the sign infront of the blue house and and the person with the tomahawk gets a bank shot by throwing the tomahawk at a very specific part of the yellow roof. Does anyone know this bank shot? I can not figure it out for the life of me and my friends wont show me:/ I need to figure out where to throw the tomahawk and its really hard):