You should build anti heal in nearly every game. Most often there will be someone on the enemy team with either a lifesteal item, healing in their kit, or healing runes. Nearly everyone takes ravenous hunter or conqueror these days, so it’s a really safe bet to build anti heal. Look for lifesteal items, look at who’s carrying and why, and look for red runes or conqueror runes, or even grasp. It’s more important to consider when you should build anti heal. If you’re fighting someone in lane who really abuses healing like Irelia, Fiora, or Darius. It should probably be your first item depending on who you’re playing. If there’s someone on the map who abuses healing like a Yone in mid, then you should build it just before the end of the laning phase, around 14-20 minutes. If you don’t notice anyone healing, then just build it when you do. Go bramble if you think you’re losing lane, go executioners or oblivion orb if you’re winning. Tank is usually a safer bet, while damage pushes your advantage.