I see you didn't read the guide; I wrote it so you never be alone (since its almost useless) and always stick to one of your teammates (lane or jungle).

There is no major reason to max Stormguard, since it will deflect 10% of Catherine base HP (HP without gears, ie. 77 + 7*Lv) on every level. Higher level of Stormguard will only raise your burn damage and lower its cooldown a bit, and since you shouldn't use this ability offensively, Stormguard shouldn't be maxed instead of Merciless Pursuit or Blast Tremor.

On the other hand, Warhorn will help you secure kills thanks to its active ability and will reduce your cooldown (more stuns). Usually I rush Warhorn since its cooldown is way lower than Crucible, which is way more useful because early game you get into fights more often rather than mid-late game.
Unless there is a hero which ultimate can change the way of a fight, I do not rush Crucible over Warhorn. It's highly situational and the reader should know not to follow any guide 100%, but to take its information in mind.

Thanks for the comment!

Don't rush warhorn, you wrote this guide making sound like you reject your teammates and try to win the game yourself. Every good support should have a Crucible and Fountain of Renewal by 20 minutes.

Also you SHOULD max Stormguard, as it will deflect greater damage and discourage others from hitting you, especially in close call chases.

Glad you see the point of an offensive item. Check my build http://www.vaingloryfire.com/vainglory/guide/catherine-the-annoying-pest-amp-pummel-build-9406

Last updated, right now.

Changed Metal Jacket to Atlas Pauldron and removed Clockwork to add Aftershock thanks to the first comment.

Enjoy!

It's true that this build holds no offensive item for Catherine, I will work on that. Nevertheless, this build is not focused on receiving damage but to support your allies, as you will understand once you read the whole guide. I think the build is a small portion on the things needed to win a match.

Thanks for your response!

Looks like you wrote a whole lot but with no items for offense you are as annoying as a gentle breeze. Sure lots of defense with a stun but in reality the only way this build would work is if the enemy targets you while your team does the killing. The enemy could counter this whole build with a single defensive item. You would do no damage to enemies. Kudos on the guide but a lot better builds for Catherine.