Unless you cheat it is impossible.
Not in Platinum but in HG/SS you can
You can't catch rayquaza in platinum unless you migrate it from ruby, sapphire or emerald.
you have to migrate it from emerald,ruby or sapphire.
Sky Pillar
on eBay you can buy Pokemon platinum for $1.05 with all of the legendaries unless you use action replay for a code!
you need the Pokemon modifier cheat
how do you catch a mewtwo on Pokemon platinum
Wild Rayquaza can only be found in heartgold/soulsilver. Either catch it in one of those games and trade it to Platinum or get one from the Global Trade station (Jubilife city)
you cannot catch the 3 regi's in Pokemon platinum you have to catch them in Pokemon emerald then transfer them to Pokemon platinum. thnx
depending on the game there r certain Pokemon u cannot catch like say on emerald u cant catch palkia or dialga so on diamond u cant catch raquaza sorry
Migrate it into Pal Park.
kyogre,groudon,raquaza and jirachi