Now follow Sam by climbing and jumping, as you did before. You will get to a passage, where you can't follow Sam. Nate will say: "I can't jump that high". Climb to the right and up the shutters to get to Sam. Next tricky bit is the free fall ledge. After Nate drops down, he will glide down the roof. Make sure you make him slide on the left side so Sam can catch him, when you jump.