Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Is build is geared to cause great harm to their ultimate and make the front row for his team, as well as cause massive damage with their skills as Resulut Smite, and Righteous Gust
Gallium has a wide range of items that can be useful for him, but as the focus and tanking and buy time for his team to burst the enemies. I recomend Sunfire Cap and Spirit Visage as indispensable items for during your ultimate damage from Sunfire along with the recovery Bulwark improved with Spirit Visage will cause you to remain longer in the fight and cause but damage. Thornmail is very attractive if there are champions like Tryndamere and Vayne.
Start the fight with a Smite Resolute to slow your opponents followed by a Gust Righteous to earn additional movement speed facilitating their approach, use itself the Bulwark to increase his armor and magic resistance, use your ultimate while the ability is active, this is critical because while you are receiving enemy attacks you will be healing. Take care when using your Ultimate because it can be easily turned off by control group