you get all 8 badges, defeat elite 4 (including Steven go to pacifidlog something like that (route 131) surf right, then when you pass two trainers go up. Then there should be a path of rocks (on the water) bringing you towards the cave entrance. You go into the cave and pass the brown colored floor stage (it's easy) then when you get onto the sand, go up and there is another cave entrance (The tower) You enter that and you should see cracks on the second floor. If you don't have an Acro bike, your fine. You get on your bike to get over the cracks. Be warned though, if you go too slow on a crack, you'll fall through. It might take some time to get pasted, but you'll get there. Then on the top floor is Rayquaza.Make sure you have nearly 50 each of:Timer balls,Repeat balls,Great balls,Ultra balls,100 poke balls and a master ball if you have more than one.Rayquaza is one tough cookie........:)
Good Luck on Your Quest!!!
Your wrong you can get rayquaza before elite four at the same place after you beat all 8 gym leaders
Actually you can get rayquaza right before you face the 8th gym leader (after you go to it in sky pillar and it scares away groundon and kyogre) it return there and you need the mach bike and a lot of ultra or repeat balls