Pros:
1.Good lane sustain
2.High early and mid game damage
3.Only has one skill shot
4.Can ignore all CC with his ultimate

Cons:
1.Squishy early compared to most top laners
2.High mana costs on his Undertow
3.Has a skill shot
4.Everyone will CC you after your ultimate

Passive ( Berserker Rage): Not much to say here. Olaf's passive gives him more attack speed the lower his HP is. This means that if you save his W until you're half HP or lower you can get the most use out of it and win fights even harder.

Q ( Undertow): One of Olaf's high damaging abilities. Undertow is a simple straight line skill shot that has variable end range that slows and damages all targets it passes through. This means that the axe only goes as far as the mouse cursor and does not pass through to its maximum range unless your mouse is at its maximum range. It's a good idea to practice throwing the axe just far enough to hit your target and no further because if you run over the axe on the ground you pick it up again reducing its cool down significantly. This allows you to chase and deal absurd amounts of damage without auto attacking much. This skill can also be used to wave clear, but costs lots of mana when you spam it. We often max this skill first to chase down and kill our pitiful opponents as they attempt to flee from our fury.

W ( Tough It Out): This is Olaf's sustain and one point wonder ability. This ability gives him a moderate attack speed steroid and increases Olaf's healing for a short duration. This is all healing affects including passive health regen, health regen from potions, health regen from items, health regen from heals from allies, and lifesteal. If you have a flask in lane and are full mana while you are trying to heal up, drink a flask charge and press W to maximize your sustain. Also try to use this ability when low and fighting an opponent. Not only will the attack speed count for more (because it stacks with his passive) but most opponents will try to stay and fight you if they see you are low, killing themselves on your sustain.

E ( Reckless Swing): The second of Olaf's high damaging abilities. Some things to note, the damage is true damage which is why I recommend maxing it against tanky melee champions in top lane (like Sion) over maxing Undertow. It scales off of AD, but its cool down is also reduced by 1 second for every auto attack you perform. This means that you want to build AD to maximize it, but you also want to auto attack as fast as possible to use it more. It also requires HP to cast, dealing a small amount of damage to yourself based on how much damage the ability does so be careful not to drop yourself too low using it. If the ability last hits the target it refunds the HP cost so don't be afraid to last hit with it if you are going to miss a CS otherwise.

R ( Ragnarok): This is a two part ultimate. It passively gives Olaf armor and MR which is why you want to build Black Cleaver early. The HP from Black Cleaver is even more effective because of the free resistances Olaf gains from his ultimate. When activated, the passive armor and MR go away and instead Olaf gains an AD steroid as well as a movement speed buff and ignores all forms of crowd control. It's a good idea to wait to activate his ultimate until a CC effect hits you to maximize your CC negating capabilities and also allow you to be as tanky as possible for as long as possible with the passive component.

1. Marks: Greater Mark of Attack Damage is simply the best choice for Olaf. Both his Undertow and Reckless Swing have high AD ratios and he has enough attack speed steroids that you don't need more in your runes.

2. Seals: Since you'll be playing Olaf either top or jungle Greater Seal of Armor is a must have. If the enemy top laner is AP armor seals are still a good choice to help you tank minion and tower damage.

3. Glyphs: You want to have 6 Greater Glyph of Cooldown Reduction because with this build you will have 30% CDR from items and 10% from runes and masteries allowing you to hit the CDR cap of 40%. Olaf relies heavily on spells for his damage and having his ultimate, Ragnarok, up as often as possible allows him to make big plays.

The remaining 3 glyph slots can be used on either Greater Glyph of Scaling Magic Resist or flat MR to make you a little bit tankier in team fights later on in the game.

4. Quintessences: Again, the Greater Quintessence of Attack Damage is the best choice. Additional attack speed is unnecessary for laning and there are no other Quints I would even consider on Olaf.

You can play Olaf one of two ways, either full tank, or damage threat. If you want to carry your team rather than just be an annoying wall of slows, you're going to want to be a damage threat and that means taking 21/9/0 in your masteries. This is generally just better for laning as well because you will want to trade back with your opponent if they fight you and offensive masteries allow you to do that better than defensive ones. If you really want to be a tanky beast late game you can try switching these masteries around to 9/21/0, but that's not my play style.

Starting Items: Crystalline Flask and potions are basically always the best start. There are very few scenarios where you would want to get something else because Olaf needs the mana early and you don't get Tough It Out until level 4 so before that you have no innate sustain.

First Back: You want to have at least enough gold for a Phage before backing. The health, flat AD, and movement speed all synergize amazingly with Olaf's kit. They allow him to deal more damage, be a little tankier, and chase down pesky opponents. If you can't afford a full Phage on your first back then just pick up a Long Sword and a Ruby Crystal along with a few health potions.

Mid Game: You're going to want to finish your Black Cleaver and go for tier two boots. Your two choices are Ninja Tabi or Mercury's Treads depending on what the enemy team has. Even though Ragnarok prevents Olaf from being CCed at all, it only has a short up time and Mercury's Treads are a better choice against heavy CC team compositions especially if your lane opponent does magic damage. Next you'll want to be looking for your first tank item. Generally this will be a Randuin's Omen unless again your lane opponent is AP in which case you'll go for a Spirit Visage instead.

Late Game: At this point you should have your tier 2 boots, Black Cleaver, and either Randuin's or Spirit Visage completed. Next you'll want to start itemizing for defense against both magic and physical damage. So if you went for magic resistance earlier you'll want to get a Randuin's Omen next, or if you went for armor you'll want to get a Spirit Visage. Next you'll want to be considering damage or more tank stats. If the enemy ADC is fed get a Thornmail, if the enemy has fed magic damage dealers get a Banshee's Veil, if you're fed get a Ravenous Hydra. Generally speaking you won't get both Banshee's Veil and Thornmail, but one or the other and Hydra to end the game.

Final Build: Your final build should be Black Cleaver, Mercury's Treads, Randuin's Omen, Spirit Visage, Ravenous Hydra, and Thornmail/ Banshee's Veil. The reason why I say Merc Treads rather than Ninja Tabi is because late game you should replace the Tabi with Merc's even if you started with Tabi. Ultimately the Tenacity is much more important than the tank stats from Tabi and if you need to defend against an ADC you should just have a Thornmail and Randuin's Omen anyway. Often times I'll switch my Tabi for Mercs after completing Hydra even before I get a 3rd big tank item if I need them.

Olaf is a beast, but a lot of champions can duel him at levels 1 and 2 because he is forced to start Flask instead of a combat item. To avoid this you should take teleport and do a jungle camp at level 1. I suggest starting either Wolves or Raptors, depending on which one your jungler wants you to take. Start Undertow and spam axes into the camp while autoing the large monster and chugging your flask. If you dance around and pick up the axes after you throw them you have one of the fastest camp clears in the game and should stay above half HP the whole time. Then you simply recall, buy an additional 2 HP pots for a total of 5, buy 2 Mana Pots, 1 Green Ward, and TP top. You will be level 2, your opponent will be level 1 almost 2, and the wave will be pushing towards you. At this point you allow the wave to continue pushing without fighting your opponent until it gets to your tower. Use your E and W to last hit under the tower and regain any HP you lost from harassment and now the wave will be pushing out. If you played this correctly you will have an XP advantage over your opponent and you can start attacking them while the wave is pushing towards their tower. By the time the wave gets to their tower you should have TP back up and you can either recall for a Phage and TP back to lane before they can push back and keep them in lane, or just recall and save your TP to gank bottom lane later. From level 6 onward you should look to harass with a Q/E combo (do not autto attack or else you will draw creep agro) and once they're down to about half HP you can pop Ragnorak and kill them if they aren't already under their tower.

Olaf's mid game is insanely strong. Mid game is generally the point after you have completed Black Cleaver and tier 2 boots. At this point you should be looking to TP gank other lanes, or simply walk down to Dragon with your jungler and stir up trouble. If you have Ghost and Ragnorak available it should be easy for you to go to Dragon, start it, and then when an enemy carry (ADC or mid laner) tries to stop you, pop Ghost and your ult, hit them with an Undertow and proceed to kill them before they can make it back to a tower. After which you just chug flask charges, pop W, and continue taking the Dragon as if nothing happened. Alternatively, if one of your lanes is pushed in you can TP behind the enemy players or walk down and act as a jungler and gank them from river. Olaf's Undertow is not only an amazingly strong slow, but also dishes out enough damage to make this an excellent choice. If you choose to walk down to the bottom side of the map after recalling you can also catch the wave in top lane by TPing back after the fight and lose few creeps for a potentially huge advantage.

Despite building tanky, Olaf is still going to be difficult to team fight with. Most enemy teams will try their absolute best to kite away from you while you rush headlong into them and with ******ed champions like Kalista and Tahm Kench being added to the game, they will often times be successful. Therefore you should consider split pushing when your TP is available. Olaf is an amazing duelist (even capable of dueling champions like Jax and Nasus) and with his multiple attack speed steroids, wave clear, and sustain he can put a lot of pressure on the enemy team just by being on their half of the map in a side lane. If you are going to split push you absolutely must have an upgraded yellow trinket with two ward charges and be using them so you can back off without dying or using your ultimate and ghost to escape. Then it's a simple matter of pressuring towers while your team sits as 4 in mid lane. If a fight breaks out TP behind the enemy team and start killing carries. Flanking is Olaf's best friend.

If your team is too weak to pose a threat without you present, or if the enemy team has someone you can't duel, then you need to be with your team, but in the jungle just to the side. This is because Olaf wants to have the enemy team engage on his own team before fighting. If the enemy team is too busy running into your's they won't have the time or the ability to think about running away from you. This makes your job much easier. Now it's just a matter of deciding if you want to kill the mid laner or the ADC.

In general you never want to be the one to initiate a fight because you aren't a full tank and the enemy team can kill you if you get focused. Flanking by either positioning off to the side or TPing behind the enemy team is the best way to fight. You always want to focus a carry or the most fed player on the enemy team and kill them before your ultimate runs out. Once your ultimate is down, Ghost has expired, and you get down to half HP, back out and throw axes at priority targets to help peel and deal damage safely. These targets can be carries that are running away or assassins trying to kill your carries. Your target choice depends on your positioning, but in most cases it's a good idea to kill the assassins and bruisers trying to kill your carries.