Quite simple,You can't!! I tryed once and I couldn't hope I helped..
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.
Unless you cheat it is impossible.
you have to migrate it from emerald,ruby or sapphire.
on eBay you can buy Pokemon platinum for $1.05 with all of the legendaries unless you use action replay for a code!
Migrate one from ruby, sapphire or emerald then capture it in the pal park.
The only way to get Rayquaza is to go to the trading center in Jublife city
Well, you cant find one in the wild. You can migrate one from Ruby, Sapphire, and Emerald.
I only know two ways to catch raquaza in only platinum first you can make your way up Stark Mountain and right before you enter the mtn. run in the big patch of grass while using your pokeradar and the other way is if you know where Prof. Oak is you have to (have Lugia, Moltres, Zapdos, and Articuno for this to work) talk to him and he says "Ahhh (whatever your name is) I remember seeing Groudon, Raquaza, and Kyogre have entered the region."
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)
Not very likely especially if you are going to get a Platinum Supreme Victors pack.
Raquaza