[Lucid:]

Usually Atma's Impaler is a noob trap. It only grants 15 AD per 1000 health. That's 45 ad if you have 3000 health which is about the average amount for a tank.

On a tanky champion, you're almost always better off building CDR if you need more damage, so you can use your spells more often. The base damage and the crowd control on your spells make it more worthwhile to maximize spell use over attack damage. CDR comes bundled with more health in Kindlegem and its upgrades or with armor in Frozen Heart, giving you the added benefit of being even more tanky while you disrupt the enemy team.