By redigas, do you mean Regigas? And no Regigas is a legendary. No Pokemon evolves into it.
There is no Pokemon named regigas. so there is no code.
you have to go to mystery gift and go to wi-fi connection and you will get a regigas gift from the pokemart.
you can't
It will be at the hippowdon temple
aegis cave
you have to connect with other game versions
Lv 70
regigas
in the temple place in snowpoint city
you have to migrate from Pokemon emarld
Regigigas doesn't exist in sapphire.