I think HP Ice would be better on this set. Gligar and Band Flygon are both immune to Spikes, meaning Roar doesn't really help against them. HP Ice sure does though.Raikou @ Life Orb / Leftovers
4 HP / 252 SpA / 252 Spe
- Hidden Power Grass
- Calm Mind
Roar raikou is pretty awesome with hazards, he can phaze all his checks ( Rhyperior / Pert / Snorlax..) until they are weak enough to get demolished by tbolt / hp grass +1. They're is not a hundred pokemon to counter him so you can't quickly phaze out to a pokemon that can't no nothing against Raikou, and set-up a calm mind, after SR+spikes you can be sure they won't tank nothing from you.
(You'll need a way to kill Flygon and Roserade since you don't have hp ice )