I like starting either boots or brawler gloves, then building the glove into avarice, and getting t2 boots. Usually defensive ones. If im doing fine and dont need the extra hp I work on brutalizer, then phage (switch those around depending on how you are doing) and get Frozen Mallet from there and the rest is just counterpicking. Items I like for him are Maw and Atmas (defense and crit chance for his E). I use my E as my main dmg source. If you are facing someone like rengar, ignite really helps because you can ult ignite him so that he doesnt have a chance to stealth away (this works for champs like shaco as well, but the silence should be enough for shaco since they are generally squishy.)

So boots, yomumus, IE, FM, Atmas, Maw is my favorite end game build. Always look at your death recap though. Plan accordingly.

I like to build him tanky. And for closing the gap, remember his Q gets you out of slows and stuff, and also gives you some nice speed. His e is great for speed at the beginning, but it tends to slow you down if your fast enough late game. His w can be used to tank or turret dive. My favorite part is that his ult has a bit of range. For example, once i was in jarvan ult and was about to die. Then varus came with low health and started shooting, so I was able to ult him right before i died. He laughed so much in the all chat. XD i like to initiate with his q for speed and silence

all depends on the gold you go back with your first buy, and whos on the other team. heavy ap, build hex early. tanky bruisers, built brutilizer. building gp5 items is ALWAYS a good idea. i like to rush hog an avarice on garen since they both work so well with his passive/skill set. in 3s, you HAVE to deal damage. if you dont, you're useless. at the same time, if you're going to die after being focused for 3 seconds, you're useless too. garen is all about doing enough damage to kill everyone, and being able to do it right under their turret.

just remember this simple rule. if you dont win with garen, you're not yolo'ing hard enough.