you deafeat Maxie @ Magma hideout and archie @ aqua hideout
No you do not need the regis to open sky pillar it is actually open before you even go to the Pokemon league and rayquaza starts on Lv. 70
After you defeat Team Aqua and Team Magma's bosses, Wallace will take you to the Sky Pillar to awaken Rayquaza. Going through the incident in Sootopolis City, you can afterward return to the Sky Pillar to catch Rayquaza. This time, Sky Pillar will be more difficult to travel through, and Rayquaza is Lv. 70.
Sky Pillar will not open until it becomes essential to the storyline. Once this occurs, Wallace will meet you at Sky Pillar and grant you entry in order to awaken Rayquaza. After completing this event, Sky Pillar will remain open. From the second visit onwards, the Mach Bike is required to navigate to the top floor. Just go there after you get through Groudon and Kyogre's battle.
do the Pokemon leuge then talk to the weather dude and he will open two new places to fly to groudons cave and the sky pillar then fly to the sky pillar at the top raquazer awates
You need to beat the Elite Four.
Go to sky pillar which is located on route 131 go to the top where you see raquaza and then he will fly to sootopolis. get out of sky pillar and fly to sootopolis and then.....
Go west from Route 129. You'll meet some trainers, continue on to Route 130, and find the Sky Pillar in the middle of Route 131. Sky Pillar will only be open to you after you defeat the Elite 4.
At the very top of Sky Pillar.
wake up raquaza in the sky pillar
after you beat the elite four the door at sky pillar should open
sky pillar on the sky pillar on rt 114
the route that sky pillar is on is 111 above the town Mavville city. the sky pillar is in the desert hope this helps