Braum need more cooldown reduction to own all the damage of the enemy's shot and more defense to protect him adc. I think that this build is so usefull to be rlly usefull in teamfight in late game.

Braum need the q early to stun and do first blood for the adc is so usefull the e too but it need only for the ulti of most powerful champ like ezreal or lucian or miss fortune or maybe all adc :D.

I haven't nothing to say to the masteries.

The most important thing for a good tank support are health magic resist and armor.