To obtain Raquaza in Sapphire, after defeating the Pokemon League, or the Elite Four, go to Pacifidlog town. From there go to the route to the right and scan along the top area for openings. When it's found you shall find an island with Sky Piller on top of it. You will definately need a mach bike to go over the cracked parts of the floor. When at the top of Sky Pillar, you should see Raquaza. Make sure to bring many poke balls and a strong pokemon that knows hypnosis. Weaken Raquaza the use hypnosis to make it much easier to catch. By the way, Raquaza is level 70.