The story now jumps back in time, exploring Nate's childhood where he seems to be getting into trouble at an early age.
After jumping out the window and following the roof right over a small ledge you'll notice that the roof to the left is too steep for Nate, who doesn't hasn't had years of honing his impressive terrain skills at this point. Climb the air conditioner unit and use the small decorative ledges to climb up and over the wall and then hop back over the ledge when you're on the other side of the roof's slope.
Enter the window on the adjacent roof and open the door straight ahead by pressing Triangle. As you head down the hall a priest and the nun will enter the room ahead, so stick to the left side of the hall and take cover by pressing O.
When they both turn away from you, hold up on the Left Analog and press O to rush around the corner and then quickly take cover behind the white desk before the two turn around. From here, wait for the conversation to end and the nun to open the door on your left and then head into the room on the right if you want to see Nate's file.
Follow the nun into the next room and take cover behind the row of bins straight ahead and then follow it right, holding up on the Left Analog and pressing O to head around the corner.
Wait for the nun to stick her head out the window as she smokes and make a run for the plaid couch to the right and enter cover again and then turn the corner and wait at the edge of the end table. Wait until she pokes her head out the window again and then make a run for the window on the right.
Press O to drop from the window ledge to the ledges below and shimmy left to reach the side of the roof and climb up.
Follow the roof and jump across to the adjacent building and then hop up to the ledge and shimmy right, while pressing X to jump across the gaps. You can now hop to the drain pipe and climb up to the roof to examine the backpack by pressing Triangle.
After the cutscene follow Sam across the rooftop and climb the chimney, using the Left Analog and X to back jump from the chimney to the opposite roof. Hop over the railing to slide down the roof and then hop over the ledge to the left for a cutscene.
The grappling hook is a new feature in the Uncharted series and it comes in handy throughout the game. After Sam climbs up, press X to grab the rope and then hold L1 while pressing up on the Left Analog to climb up.
At the top you'll need to shimmy left around the ledge before you can pull up and then continue to follow Sam across the rooftops. Make the leap across the huge gap, barely making it to safety, and climb up the ledges and then shimmy along the outside of the ledge and jump across the gap.
Crawl under the green netting and continue to follow Sam across the rooftop, swinging on the cross, and then grab the rope from Sam by pressing Triangle and swing across the gap, pressing X to release.
Jump across to the adjacent building and then jump again to the ledge near Sam, but since Nate can't reach the higher ledge he'll have to go around to the right before he can climb up to the steeple.
Follow Sam across the roof and up the next tower and then watch as he slides down the roof and jumps at the last second to reach the opposite rooftop. Follow suit by shimmying to the end of the post and then drop by pressing O, but make sure you don't press X too early or you'll miss the jump.
Circle the roof and grab the grappling hook from Sam and press L1 to make a line to the telephone pole. You can now jump and swing to the fire escape and climb down the ladder for a cutscene.