After you get across the barbed wire and onto that ledge get in line with the small roof of the next house, sprint and jump and you should make it onto the next house and be in thin air.
Then walk onto the water barrel and look towards the block of flats (just left of the balconies and left of where you just came from).
Sprint a few step over to that building then jump. This bit is hard !! When you make it to the roof go to where the balconies are and jump onto the on a bit higher than the building. When you get onto the balcony walk along then jump onto the next one along.
You should see some wire fence on your left jump onto that and walk along to the next building. From there it is easy to get onto other rooves. Remember old school mode.