Sup. I'm Goregasm, and this is my guide for Leona.

The builds above are mainly the same. They only differ in skill sequence.
Team 1 for a duo lane, Team 2 for a solo lane.

The aim of this guide is to build Leona as a tank with heavy emphasis on CDR but without sacrificing her durability in teamfights. This allows her to initiate and soak up damage, but also to continuously disrupt teamfights with two CC abilities on a very low cooldown.

Some may find it strange to opt for CDR on Leona. My reasoning for this is best described by comparing her to Amumu (with whom she is often compared anyway). While the CDR on her Shield of Daybreak is identical to Amumu's Bandage Toss, Leona doesn't have much to do in between cooldowns to damage targets, peel enemy champions off your carries or disrupt teamfights. Amumu, however, has his Despair up constantly doing significant %hp damage, and a low CD Tantrum to spam.

Furthermore, Leona's passive, Sunlight, means that your allies will be dealing more bonus damage to targets based on how often you can output your skills.

People seem to think that because she deals very little damage, she doesn't present herself as a threat and that they need to add some damage to her. Firstly, it's wrong: she has ****loads of CC and this makes her enough of a disruptive force in teamfights that people will feel she needs to be removed. And if they don't, you stop them from attacking someone else. Secondly, her AP ratios are terrible (for those building AP), she has no AD ratios on her abilities (for those building Atmog's), and if you want to build her as a Trinity Force tanky DPS... then why the hell aren't you playing Jarvan IV or Irelia?

Pros:

• 3 forms of CC, 2 on 8-9 second cooldown at max rank (and even less with 35% CDR)
• Powerful and mobile initiator
• Able to disrupt targets multiple times during teamfights
• Her passive encourages teams to focus down important targets
• Powerful laning phase (more so than many others tanks)
• Shield grants increased durability
• Her Valkyrie skin

Cons:

• Low damage
• Low AP scaling
• Not viable to jungle (very, very slow)
• If placed in a solo lane, her low damage forces her to play passively
• Her masculine voice can make masturbating and playing at the same time difficult

As you can see from her pros and cons, Leona's low damage and AP scaling make her non-viable to play as a tanky DPS / offtank / bruiser. However, her many forms of CC and durability make her an excellent "pure tank": building pure durability and CDR to maximise her CC.

Greater Mark of Magic Penetration: Mainly just because your choice of marks is fairly limited, and your damage output is mostly magic damage.

Greater Seal of Armor: For some early game resilience (hur hur) vs. AD champions, minions and towers in your lane. I prefer armour over dodge just because dodge does nothing to mitigate physical damage abilities, just autoattacks.

Greater Glyph of Magic Resist: For some early game durability vs. magic damage harass in your lane.

Greater Quintessence of Health: This build skips Doran's Shield as an opening item, and so you still need some source of HP for your laning phase. This provides as much as you can get.

Greater Mark of Armor / Greater Mark of Magic Resist: If you think that the magic pen is a waste and want to focus on even more resistances, pick either of these two.

Greater Seal of Evasion: If you're a fan of dodge instead of armour seals, grab these instead. You'll just have a little more trouble in both the lane and in teamfights vs. champions with physical damage abilities.

Greater Glyph of Cooldown Reduction: With the items in this build and these runes, you'll hit just over 40% CDR. However, you will lose early game mitigation versus magic damage.

Recommended

Exhaust

I run Exhaust with most of my non-jungling tanks because of the amazing utility it gives you. Exhaust has both offensive utility in locking someone down and reducing their resistances so that your team can destroy them and defensive utility in case your abilities are on cooldown and you need to nullify someone's damage output to protect your carries.


Flash

Once again, I like Flash because it has both offensive and defensive uses. Flash works great defensively as a Get Out of Jail Free card if you're caught in a bad position. However, Flash + Zenith Blade also work brilliantly in conjunction to secure retreating targets.

Situational

Ghost

Another potential choice over either Exhaust or Flash. However, I prefer Flash over the two because it tends to either save my arse more or secure kills better than Ghost can, and if you swap this out for Exhaust then you're swapping even more CC for increased movement speed.


Teleport

An entirely viable option, particularly as such a CC heavy champion that can decide teamfights. Just not one of my favourites.

I run 1/21/8 for a number of reasons.

21 in Defense: As a tank, it's important to maximise your damage mitigation. Strength of Spirit is very important, not just for the laning phase, but because of the insane HP5 granted from the large amount of mana from Frozen Heart and Banshee's Veil.

8 in Utility: I opt to go 8 in the Utility tree for 3 points in Good Hands, 1 point in Perseverance and 4 points in Awareness to keep up in XP or gain an advantage. For why Good Hands is generally better than Perseverance on any non-healing, non-regen based champion: do NOT get Perseverance! @ leagueoflegends.com

1 in Offense: Finally, because we're taking Exhaust, we may as well improve it and give it extra offensive utility.

Skill Sequence depends on whether you're in a solo lane or duo lane, and also if you think a level 1 teamfight will break out.

If you're in a duo lane, pick either Shield of Daybreak or Zenith Blade first to shut down an enemy champion. Your Shield of Daybreak + Exhaust + whoever you're laning with can grant a first blood if your teammate is heavy in level 1 damage. Max Shield of Daybreak for a lower CD on your stun, then Eclipse for more durability and finally Zenith Blade to lower its CD.

If you're in a solo lane, you won't have the damage to follow up your CC to kill anyone in the lane. Also, you attack slowly and do no damage, so if your lane opponent is push heavy you may find yourself struggling to keep the minions off your tower. Pick Eclipse first for durability and harass, then the rest of your abilities by level 3 to maximise the chances of success if your jungler / roamer tries to gank your lane. Max Eclipse first for farming, durability and harass, then Shield of Daybreak to lower the cooldown on your stun, and finally Zenith Blade for the lower cooldown.

IMPORTANT: If you're participating in a level 1 teamfight over jungle buffs, take either Zenith Blade or Shield of Daybreak first. Different situations may call for different skills to be picked first: generally, Shield of Daybreak for defensive situations, and Zenith Blade for offensive situations.

IMPORTANT: Tanks need to be versatile in how they build, more than any other type of champion in the game. Ranged AD carries can follow specific builds to maximise the output of their damage; the only choice they usually have to make is whether to build Last Whisper or Black Cleaver.

As a tank, you need to be looking at the biggest damage dealers on their team and build accordingly. You need to know the damage types of the champions you're dealing with and the items they've bought. And then, you need to build to mitigate that damage accordingly. If you go up against an all AP team, don't buy Frozen Heart for the CDR. As the team's main tank, your durability comes first and your utility comes second. Suck it up and build accordingly.

This build and the build order assumes that you're going against a balanced team. If their Annie is getting ludicrously fed but the rest of their team isn't, try building your Banshee's earlier, even if it means sacrificing some of your CDR until later.

Also, never, EVER build Sunfire Aegis. It is the worst tanking item in the game. Comparing it to the other HP + armour item, its stats are worse than Randuin's Omen, and you're trading CDR, HP5, the on-hit slow and the amazing AoE slow and AS debuff active for... 35 magic damage per second. Which will actually end up being less because you have a glorious 8.55 magic pen. If you want to get a Sunfire because you don't remember to use item actives, then LEARN to use actives. They win teamfights.
Potentials for starting items include:

Regrowth Pendant + Health Potion: Because I like to go for an early Philosopher's Stone for lane sustainability and GP10, I like the Regrowth Pendant and Health Potion. Plus, it allows you to hang around as a threat while taking some harass and then just regenerating it all back by retreating momentarily.

Cloth Armor + 5 Health Potions: This is probably more for when you're going to be stuck in solo top against an AD champion with heavy harass. It will stall your Philosopher's Stone, but later it will build into your Aegis of the Legion.

Boots + 3 Health Potions: If you think you'll be in a duo lane against soft, easily gankable targets with poor early game harass and you and your laning partner are confident in killing them, pick this for increased manoeuvrability with 3 health pots for increased sustainability.

You should look to complete these basic items as soon as possible.

Philosopher's Stone: The high HP5 and MP5 gives you great staying power in the lane, and the GP10 helps your lackluster farming and allows you to give more CS to your laning partner.

Mercury's Treads: Simply the best all-purpose boots for a tank, for the largest CC reduction of any item in the game, and especially because AP carries tend to have the greatest damage mid-game.

Aegis of the Legion: I'm not sure why tank players don't buy this item. It builds out of simple, cheap components, it is cost-effective for its stats (remember, you get the aura too) even when ignoring the fact the aura affects other people, and you're mitigating the damage of your team just by standing around.

At this point, your build's pretty standard for a laning-tank build. You probably have more MR than you do armour, and we haven't got any CDR. We solve this by building your core items in the following order:


Glacial Shroud: Your armour is lagging behind your MR at this point, so not only does this rebalance your resistances, it adds 15% CDR to your target of 35%.

Kindlegem: This not only gives you a little extra bulk, but it's a cheap source of CDR. This item brings you up to 25% CDR.

Frozen Heart: This item is amazing. AD champions should now have trouble damaging you and your CDR is at 30%. The aura from Aegis of the Legion and Frozen Heart means that just by existing in a teamfight, you're swinging the fight in your favour.

Banshee's Veil: Once again, you're a tank, and your durability comes before your utility. Make sure you build this as your scaling armour and recent investments in Frozen Heart have meant that your MR is now beginning to fall behind. Even though Banshee's Veil gives you less MR than Force of Nature, the HP that comes with it grants you more effective health vs. magical damage AND it gives you a spell shield. Sweet.

Shurelya's Battlesong: Even though it lacks damage mitigation, I consider Shurelya's Reverie an overlooked item for any tank that benefits from CDR. The active is great when initiating teamfights or helping others to escape ganks (remember that as a tank, you exist for your team). Complete this for a little more HP, HP5, MP5, 5% CDR (bringing you to 35%) and that cool active. It's only costing you 550gp.
My sixth item is blank for a reason. At this point, complete an item based on whoever constitutes the biggest threat on their team.

Force of Nature: Against a team where the kills are balanced, or where their AP carries are more fed than the rest, build this. By this point your armour exceeds your MR by 58, so against a balanced team, this is what you should build next. It should equal out your armour and MR values and mitigate a great deal of the damage any of the AP carries are dealing.

Randuin's Omen: Get this if their AD champions are dealing most of the damage. It's the best AD tank item in the game, and the only reason we didn't take it earlier is because we wanted more CDR. The active on it also synergises well with Leona's kit ( Zenith Blade + Randuin's Omen + Solar Flare + Shield of Daybreak = enemy team is never ****ing moving).

Thornmail: If it's a late-game squishy autoattacking AD carry who's the problem ( Tryndamere, Master Yi, Ashe, Tristana, Vayne, etc.), consider getting a Thornmail instead. They'll kill themselves before they kill you, and you should have enough CC to lock them down for your team.

Generally speaking, you should be last hitting with your autoattack to farm whether in a solo or duo lane. If your lane gets pushed too far back to your own turret for your liking, use your shield to weaken the minion wave.

If you open up with the shield in the duo lane, your laning partner is likely to look at all the shiny low HP minions, liken their luminescence to the gold that will spew forth from their rotting corpses, and take it before you can because of the bonus damage from your passive. While this is fine if you're pushing or if they're pushing hard, remember that you're not a support champion and that you still need CS to be useful in teamfights. Just try and share it with your laning partner.

In a solo lane, unless you're facing against a pusher champion like, you'll still want to reserve your shield for when the minions are on your side of the river. Push too hard and you leave yourself vulnerable for ganks while also preventing ganks that may have occurred if you weren't pushed so far.

In a 2v2 lane, your focus should be on gaining CS and creating opportunities to push your enemies out of the lane. Harass or kill enemy champions who go in for last hits by activating Eclipse, opening up with Zenith Blade, stunning the target with Shield of Daybreak and then autoattacking until Eclipse pops. If you fail to get the kill but they have to leave the lane, you have still succeeded. Take the opportunity to deny the other champion that remains in the lane (if any) of XP and GP, and to last hit without contest.

In a 2v1 lane, your focus should be on denying the enemy champion XP and GP with the monstrous threat of your CC. Make sure you and your laning partner only last hit. Push the lane and you'll lose your advantage. Hang in between their melee and caster minions, and make sure to punish the enemy champion with a Zenith Blade+ Shield of Daybreak combo if they go in for last hits.

In a 1v1 lane, it's unlikely that you'll be able to kill your enemy, so just focus on punishing their mistakes with harass and most importantly gaining CS. If they're pushing hard, try to use Eclipse to farm and equal out the push. Otherwise, play fairly passively and try to last hit.

In a 1v2 lane, you will only kill idiotic or cocky players. Do your best to gain whatever CS you can, though this is best achieved at your own tower, so let them push so that you aren't at risk of being killed out in the lane. If you push too far back, you risk getting denied.
Your role in teamfights is to initiate on high priority targets (their carries), soak up damage in teamfights, and repeatedly disrupt the enemy team.

Initiate by using Zenith Blade to dash to your target, and then either Shield of Daybreak if on a single target, or Solar Flare if they're grouped up. At 35% CDR, you become an incredibly disruptive force in teamfights. You should have a 1.25 stun available every 5.2 seconds, your line nuke immobilise every 5.85 seconds, and your ultimate every 48.75 seconds. Using all your abilities to apply your passive to high priority targets in order to repeatedly add bonus damage for your allies.