If you have not got a camera with you, you need to "borrow" one. Head towards the red blip for a group of tourists. Kill the one taking pictures for his camera.
Drive to the planning authority building as indicated by the map blip. Make sure you have no weapons selected as indicated by the text on the screen, as there is a heavy security presence here. Talk to the receptionist, she will tell you where to go. Go up a few floors (the staircase is to the left of the lobby behind a swing door) and go into the first open door you see. Proceed over to the elderly aircon unit and break it, you may get away with a weapon here, since breaking it with a shovel will more than likely result in a burning CJ! A fire alarm will sound, everyone will be evacuated, and guards will be distracted. Go up to the top floor and photograph the plans in the room straight opposite the staircase exit, where you can see a white model on a table in the room.
Now it gets tricky, you need a powerful weapon like the M4 and it helps if your skill is high enough to allow you to move while in the aiming stance. Head back down the stairs through the smoke, picking off the guards/police as you go, there is one round almost every turn of the staircase and several in the building lobby. After clearing the building, you will face many cops outside. Simplest thing is to just get in a car, and race back to the back entrance of the Four Dragons Casino to end the mission.
Plenty of ammo in (and practice with) the M4 or similar helps the escape.
Don't be too fat, or else you won't be able to run as fast.
Stock up on ammo for the M4 or the SMG.
Don't hit anybody in the office building.
Arriving in a fast car to the planning authority building and parking it in front of the entrance makes your escape easier.