So my Roserade has:
Item: Black Sludge
Evs: 252 Sp Attack, 252 Speed, 4 HP
Ability: Natural Cure
Hidden Power (Rock)
Sludge Bomb is a great move and has 135 base power STAB, also can poison.
Hidden Power Rock is so great as it covers 3 of Roserade's 4 weaknesses.
Rest is to heal Roserade. Switch out to awaken Roserade, using Natural Cure.
You can use Leaf Storm, and then use Rest and switch Roserade out, which negates the stat loss. Then you can repeat with 210 Base Power STAB Leaf Storm, that doesn't get weaker every time.
This is a great set and personally think the best possible Roserade set.