Yeah I have been to the rooftops,there are two ways...
1-At the begining of the level,go to where the blind skull is,except go around the other way.
2-After the part when the pelican comes,go to where the other marines are,after that look around them and you will find some big thing [can't remember] and you jum[ on it and you keep going up in this messed up building and then at the last thing to do is do a grenade jump to get to the top.
Hi I'm back