To Everyone Having Problems For What To Build
"Oh I just got one shot by an enemy Zed that went full armor pen yet I have 230 armor! I got one combo'd by a 15/0 Jayce with full lethality! I got 3 shotted by a Trynd/ADC!"
Heres the solution right here buds:
Health beats Armor Pen/Lethality (Assassins) Flat AD beats Health (Tanks) Armor beats Flat AD (ADCs) AP beats Armor (Bruisers) Magic Resist beats AP (Mages) Armor Pen/Lethality beats Magic Resist/Flat AD (MR Tanks/ADCs)
Take a good look at it, and tell yourself what you did wrong. I dont know what items counter Master Yi yet tho so good luck with that one. But for the rest it pretty simple.
If youre facing an Assassin like Jayce (Me), you dont build full armor, you build health/Armor. So
would be almost a must.
If youre facing a Mage and youre a tank, you should be building
with one or two armor items. Youre not playing for late game, youre playing for early game. That means countering your enemy as much as possible, so that you can 1v1 them no problem almost all game.
If youre facing an Armor Tank, you build

If youre facing a Health Tank, you build
Depending on whether youre playing a crit champ or not.
If youre facing a Flat Ad Champ as a Tank, you build

If youre facing mr/flat AD as an assassin, you build
(On some)
or
Youre pretty limited to your items here but this is if youre facing just squishys. Obviously if there are some tanks in the game then you'll get a Black Cleaver or Mortal Reminder/Lord's Dominiks.
If youre playing as a Mage against MR tanks, you build

If youre playing as a Mage against Assassins, you build
You want to stack health with little armor, as it counters assassins pretty hard except ones that build bork.
If youre an assassin against a Mage, you build
(if theyre vlad)
(If they stack health)
(if there is no one stacking armor hard)
If youre playing against your same type of champ, you just build normally. So are they ad? Then build armor. Are they assassin? Just build lethality and health (Edge of Night). Are they Mage? Build ap. Are they tank? Then counter tank build.
These are the correct builds (some need to be optimized with your own liking obviously) for the champs in the game. The only one I didnt do is support and jungler builds because I dont know much about those lanes to inform. People need to stop thinking armor beats Armor pen, people need to stop thinking tanks are useless. The reason why bruisers are so good in this meta is because they can stack health against Assassins, yet nobody realizes that health is great against them, and they get to have armor which counters any flat ad (ADCs) champs out there.
These are just items you need to take into consideration when you shop. Dont buy the same items over and over every game unless youre used to doing that. If you truly want to get better at this game then thats one step closer for you.