This is the first part of the Run For Your Life Mission in Hitman Absolution. In this mission you are framed for murder and must escape the police. This first part takes place on the rooftop where you have to evade some police officers patrolling the area. This guide explains how to get through the level on the hardest, purist, difficulty. It does not describe how to complete all the challenges in this area.
At the end of this guide is a YouTube video with a visual version of this guide.
When you get to the rooftop there is a police officer in front of you. Wait for him to walk around until he is stationary, then make your way to the cover next to him:
Go the the right edge of the cover and roll to the next cover. Go around it and approach the next bit of cover. Before you get too close wait for the police officer to walk past (you can just make him out through the smoke in the image below):
Make your way quickly down the stairs to the right and hide behind the next air conditioning units. There is a guard in this lower area and another guard that comes up to the top of the stars you just went down. Wait here until they both have just turned their back (the one at the top of the stairs does so after the one on the same level as you):
Then go through the door to the right inside the rooftop building. Go to the big red door with an exit sign over the top and break it open. This is the end of the first area of the Run For Your Life Mission.