Where is Giratina?

Giratina is not in Snowpoint Temple.

After you have defeated the gym leader in Snowpoint City (I always forget her name), you now have seven badges. Leave the city, and the two Galactic Grunts in front of the entrance to the Lake outside will have moved aside, so you can continue through. After an encounter with Jupiter, it's now clear that your quest is to stop Team Galactic. It's all pretty linear and easy to understand where next to go, but you'll want to head to Veilstone City and infiltrate their HQ.

Well, now if your real question it was about Giratina...how I suppose, it's platinum version...and, when you battle v.s. Giratina in the Distorsion World, ya can't battle him again in long time...when you go outside of the distorsion world, ya'll be outside of another lake, near Rute 214, and outside it'll be Cyntia...ya can't enter there...until ya defeat the Pokemon League Champion. Later, go to that lake, and find your way through the ruins, and reach to a dark place, with a portal. Enter, and you'll return to distortion world, and now, it's your opportunity to catch him (and too, get the item in there...it's the Gricaseous Orb. When you catch Giratina, and go outside of the distorsion world, it's form'll change, to Altered Form...but if ya equip hi mthe Grisaceous Orb, it'll turn to Origin form, changing his ability.

And about the Snowpoint Temple, ya need Regirock, Regice and Registeel to have acces there, and get the powerful Regigigas. Be careful, this one it's a difficult one...

(Recomm: Use Dusk Balls with Giratina, and with Regigigas, try to use timer balls...that fight's going to take a lot of time...now, I can give ya too Master Balls, just tell me, and gimme your friend code, and I'll tell you mine's, and send ya Master Balls or other items...except event only items)

In platinum after you beat the gym leader candice you go to the top of mt coronet aka (spear pillar) or later know as (Hall Of Origin) and team galatic will be there and the summon both palkia and dialga but giritina stops them in there plans my coming out of the reverse world later you go in the portal to reverse world and solve big puzzle quest and before you can fight giritina you have to fight cyrus Head of team galactic then you see something blocking your way of getting out it's giritina you have to battle it and then come out at spring path if you may make giritina faint you can find him later at turn back cave.