So I decided to make this guide because I see a lot of people playing Leona sub-optimally either by using her skills incorrectly or by building her the wrong way. This build is a pure tank build for Leona that focuses on getting as many helpful team aura's and almost capping on CDR, while still being extremely tanky. It is worth mentioning that Leona has low AP scaling on her abilities and has poor AD damage output, so it would be sub-optimal to build her as anything other than a tank. If you would like to do damage, play a different champion: do not waste your spot on the team by building Leona sub-optimally.

Please leave any feedback/comments/suggestions in the comments section, I'm open to new ideas and improvements.

When I play Leona I choose to run with armor marks, dodge seals, magic resist glyphs and health quints. While this setup is my personal preference there are several viable options for each slot.

Marks

Leona is one of the few champs in this game where it is entirely appropriate to NOT use Magic Pen/ Armor Pen marks. The fact is that Leona does not do a lot of damage and the survivability provided by armor or health Marks greatly out weighs the small increase in early game damage that Magic Pen seals would provide.

I choose to utilize Greater Mark of Armor because Armor Pen marks and quints give AD champs a large bonus in damage. These marks serve to eliminate the advantage that Armor Pen marks provide, also I tend to only get items that give armor fairly late into games so this armor provides me with enough of a boost in survivability to survive early/mid game. Plus they're cheap :)

Another viable option would be Greater Mark of Health which will give around 30 extra health at level 1 which may help lane survivability/sustainability. Personally I don't find it to be enough health to be better than armor Marks, but if you prefer health or if you are already getting armor from Greater Seal of Armor the it is a viable option.

Seals

I Think almost all tanks should be using Greater Seal of Evasion as their seals. These seals combined with masteries provide 8.75% dodge which is essentially 8.75% damage reduction from physical attacks. Dodge is an amazing stat because its benefits stack with the damage reduction of armor. Armor becomes cost in-efficient at around 150 armor, which is fairly easy to obtain. Dodge on the other hand can only be acquired in the form of ninja tabi, so you are much better off getting dodge seals, and then hitting the armor soft cap in game than using your runes to help you hit the cap.

Greater Seal of Armor Armor is armor and armor is good. Get these if you don't like the RNG of dodge or if you are too poor for dodge seals. Remeber to use different masteries if you do not grab dodge seals.

Greater Seal of Vitality These seals provide about 175 health at level 18. The way I build items I always have a large health pool and don't feel that the health is totally necessary, but again if you don't have/like dodge and you don't feel the need to have armor seals AND marks these seals are a great option. Remeber to take different masteries if you do not take dodge seals

Seals

I find that the only option for blue is really Greater Glyph of Magic Resist. Without magic resist glyphs Leona is really prone to magic damage early game.

If you would like Greater Glyph of Scaling Cooldown Reduction Would put you at CDR cap at 18 combined with masteries and Shurelya's Reverie. Could be helpful to get those extra stuns off in team fights, but not worth being squishy for AP champs.

I choose to run 0/9/21 because the utility tree is OP. Yes Leona is a tank, but the only useful things in the tank tree she is missing out on is 46 health and 4% damage reduction. By choosing utility as our focus we pick up 15% reduced CD on our summoners, 6% CDR, 3% Movespeed, some much needed mana regen, and less importantly, but worth mentioning, 1 gold per 10.

Honestly there is not much of a difference either way, and 0/21/9 is certainly viable, I just prefer the utility provided by... the utility tree.

Required

Teleport is necessary for most tanks, and Leona is no exception. This is because tanks need to be in as many fights as possible. Tank are not carries and do not benefit the team by sitting in lane last hitting minions. For this reason Teleport allows you to assist lanes in ganks, defend allies, protect turrets while people are b, and simply move rapidly across the map. Do not use it to get back to lane unless your tower is being pushed.

Good

Flash Flash is certainly not required for Leona because unlike carries, Leona does not need re-positioning to use her spells effectively like say annie or alistar would. Then again, Flash is Flash and it is amazing for closing the distance to land that key zenith-blade stun combo, or to escape a team fight while low on health.

Cleanse I personally almost never use this spell as I prefer to just get a quicksilver sash, but if you are facing a team with ludicrous amounts of CC or just like this spell over flash take it.

Fortify This spell is underrated. It can save turrets which is extremely important for obvious reasons, and, if improved via the defense tree, the AOE splash damage can be quite potent, but since I do not go that far into defense I choose not to use this spell.

Clairvoyance This spell is required in every game, its ability to provide sight for ganks, check bushes, check objectives, and check jungle camps for enemy jungler is extremely important and a huge advantage. If you do not have a support on your team or they are a douche and didn't take it, you can and should pick up this summoner. If you take it remember to improve it instead of flash in masteries.

Heal This skill is often considered noobish, but its actually quite useful. It's definately not game changing but it certainly helps in team fights, and it can be quite a surprise for your enemy in early 1v1 fights.

Exhaust This skills is both good for finishing people off as well as reducing the DPS of enemy AD carries in team fights. Definitely a necessary skill for someone on your team to have, if no one else can grab it then you should.

Bad

Ghost Leona simply is not fast enough for this skill to be worth it, she's much better off with flash.

Ignite is bad on tanks because stealing last hits from carries is bad.

Clarity Leona doesn't have enough mana issues to warrant using this spell. If you are truly having mana problems it means you are spamming too much.

LOL!

All useless: Rally Smite Revive

Every game you should be taking Shield of Daybreak first. Stuns are the most important abilities for level 1 team fights, so beyond a doubt you should take this first every time.

I then choose to get Eclipse at level 2 and then Zenith Blade at level 3 because in order to do any realistic harass you must have your 3 base abilities.

You then have two options. You can either Max your Q or your W first. I generally prefer to max Eclipse because it is the highest damaging spell in your arsenal, and it does aoe damage. Leveling Eclipse first will help you farm minions in the laning phase, and to damage multiple targets in team fights. Maxing Shield of Daybreak first is also an option because it does decent single target damage, and most importantly reduces the cool down on your stun. I personally choose not to do this because I feel like Leona is only potent when you use your abilites in a combo, it is extremely rare that you get to Shield of Daybreak multiple times without the assistance of your Zenith Blade. For this reason I find the extra damage from leveling Eclipse to be more important.

Then no matter what level Zenith Blade last.

When I build items on Leona I have 3 general goals. First, to provide your team with as many helpful buffs as possible. Second, to maximize tank stats, and third, to maximize CDR. That being said, Leona's items are very flexible and should change almost every game depending on what you are facing. The core build I use every game without fail is:

Philosopher's Stone

Why I get these items every game:

I choose to get Philosopher's Stone and Heart of Gold every game because I find gold per ten items to be extremely potent on tanks who should not be getting large amounts of kills or have an overly high CS.

Aegis of the Legion provides a potent team buff, and should be acquired by one team member in almost every game. Since you are a tank and it is a tank item, why shouldn't you be the one to get it.

Finally I always get Shurelya's Battlesong. I find this item to be severely underrated. This item provides health and regen which are obviously useful on a tank, plus much needed CDR which is hard to obtain while still getting tank items. Finally its on use is extremely potent tool for chasing/escaping. I understand it is hard to remember to use items like this, but if you focus on trying to remember to use it, you will find yourself getting extra kills and saving many team lives.

Other Items

Boots

I find I usually get Mercury's Treads. Tenacity is a much needed attribute on a tank, and the magic resist is very nice as well.

If you find your opponents are extremely melee heavy, you should get Ninja Tabi as it provides dodge, which synergizes well with masteries/seals, and armor. If you do get Ninja Tabi, and still need tenacity consider turning your philosopher's stone into Eliesa's miracle

Late Game Items

After you finish your Aegis, boots, and shurelya's miracle, you can expand in any number of ways. I usually end up picking up a Soul Shroud if a support doesn't already have it for health and a nice CDR buff for you and your team. If you want to add more utility to your build you could acquire a Frozen Mallet which provides a ton of health as well as a potent slow effect. If you need more armor you should turn your Heart of Gold into a Randuin's Omen. If you need more magic resist you can build a Force of Nature. If you are struggling with CC you can build a Banshee's Veil.

Situational Items

As always if you face a team with 3 or more AD champs Thornmail is a good investment and might be worth getting even before some of the core items. That being said Thornmail is never a worthy investment if you are facing a balanced team. It simply has too much armor and not much else; you are much better off getting Randuin's Omen which provides some health, CDR and a nice active in addition to armor.

If you are really having problems with CC Quicksilver Sash is a lifesaver.

Guardian Angel: I personally do not like this item as I feel the rez is useless 9 times out of 10 by the time you would end up getting it, but if you are one of those people who like it pick it up instead of Randuin's Omen or Force of Nature then go for it.

Leona can viably lane in two places. Leona can solo top, or she can bot with a carry. In both roles Leona should be harassing using her WQE combo. This combo works by pre-activating Eclipse then waiting a second or two for the shield/bomb to tick down, then activating Shield of Daybreak and then quickly using Zenith Blade to flash to the enemy champion. If executed properly, your Eclipse should explode while the target is stunned from your Shield of Daybreak. If you are above level 6 and are fairly sure you can kill the target, use a WQER combo by using Solar Flare right after you use Zenith Blade so that your ult stuns and damages the target right after your Shield of Daybreak stun wears off.

While laning remember to watch out for opportunities for ganks, as well as assist other lanes with teleport.

In team fights, Leona's role is to be as much of a nuisance toward the other team as possible. This means stunning enemies, and exploding your Shield of Daybreak and Solar Flare on as many people as possible. As a tank you will have to initiate a lot of team fights. This is fairly easy to do on Leona, simply wait for an enemy to get too close to you and use your Shield of Daybreak and Zenith Blade to stun him in place, either allowing your allies to hopefully kill the target, or cause the enemy team to commit to a team fight.

By the time full on team fights break out, your Shield of Daybreak should have about a 7 second CD, maybe less depending on how much gear you have. This means you can and should be using it every time it is up to stun key damage dealers or kill targets in team fights.

At this point your Eclipse takes on a more important role than simply being a damaging AOE. At max level your Eclipse provides you with a 70 armor and magic resist buff. This is why you should NOT be using your Eclipse while you are initiating a team fight. Wait to use your eclipse until you start taking damage as it will significantly improve you survivability.

You should never be using Zenith Blade for damage. If you don't need it to get closer to a target so that you can stun them, then save it for the inevitable chasing that occurs in the aftermath of a team battle.

Your use of Solar Flare is extremely important in team fights due to its potential to slow/stun several enemies at once. You should be waiting to use solar flare until as many enemy champions as possible are within its radius and you have enough allies present to do serious damage; DO NOT use it to initiate. Also if your ult is used in combination with other aoes, such as Cassiopeia's poison it can amplify the damage output of your team significantly. Finally it is worth noting Solar Flare has an insanely large range, so it is also an effective tool for chasing/ escaping especially in combination with Shurelya's Battlesong.

One last reminder. YOU ARE A TANK. While you might be able to 1v1 certain champions, you should, apart from early game laning, always be with other teammates. You are there to support your team so that is what you should be doing. One way you support your team is by carrying carries. This means that you should be letting carries get as many kills as possible, now don't let enemies escape or anything, but if an enemy is low on health and has no way of escaping, let Vayne get the kill. This attitude also applies to CS, if you are laning with a carry do not last hit unless it is impossible for them to get the kill. Another way to support the team that you can and should be doing is to ward key locations as much as possible, I tend to have 1-2 wards in my inventory at all times and place them when I see fit. While everyone on the team should be warding, you are one of the best people to do it because you can spare the gold more than a carry can. There are several good guides about where/ when to ward, so I'm not going to go into it, but it is an important part of the game that truly separates decent teams from good teams.

Finally even in mid game you are quite durable, especially with Eclipse up; take advantage of this and tank turrets for your team. Do not prevent your team from damaging a turret simply because you waited for minions to catch up.

Good luck and Have fun, hopefully this guide has been helpful :)

Please leave any feedback/comments/suggestions in the comments section, I'm open to new ideas and improvements.