If you are Op turn around to the half blown up building, crouch, go up the stairs and go through the door.

When you have done that stand on the chair, jump and you should be on the very side of a broken wall.

Then turn a little bit to the left and run and jump and hopefully you should be on a slant.

Then jump again and you will be on top of a building.

Then turn to your right and there will be a flat.

Run and jump on it and then turn left, then look down and walk on top of an object and then move to the first building.

You're floating!