Welcome to my Leona build. I bought this champ right after it was on sale and i am just in love with her. So far in my opinion she is one of the greatest tank champs in League of Legends.
I realize that not many people really like playing as a tank, but I hope that there are just a few :) If you are interested how i play Leona keep reading.
I also want to say that I'm no pro gamer with her. I don't guarantee that every game will be won. I just like playing her that way and I think that she is worth it.

Let's talk about her Pros/Cons.
Pros :
- Has a lot of CC(Crowd Control). She can stun with Shield of Daybreak and Solar Flare, slow with Eclipse and Solar Flare
- Her abilities are great for protecting allies
- Without any AP(Ability Power) items she can deal quite much damage to squish champions
- Big range of abilities, especially her ultimate

Cons :
- Mana dependent
- She is very slow (like every tank)

Sunlight
Leona's damaging spells affect the target with Sunlight for 3.5 seconds. When allied champions deal damage to those targets, they consume the Sunlight debuff to deal additional magic damage.
It is a useful passive when you are near an AP champion. So make sure you activate it as often as you can.

Shield of Daybreak
Leona uses her shield to perform her next autoattack, dealing bonus magic damage and stunning her target.
After casting your shield go for an enemy champ and stun him. If you buy items for Cooldown Reduction, you will be able to cast it over and over again :)

Eclipse
Leona rises her shield to gain Armor and Magic Resist. When the duration first ends, if there are nearby enemies she will deal magic damage to them and prolong the duration of the effect.
Try to always activate your shield near your enemies and dont let them get away before it explodes.

Zenith Blade
Leona projects a solar image of her sword, dealing magic damage to all enemies in a line. when the image fades, the last enemy champion struck will be briefly immobilized and Leona will dash to them.
It's a great skill to start a fight. First thing to do is to aim at the right target. If you are near enemy tower you might dash to the wrong enemy and end up killing under tower without any help. She will just dash through all champs and be far away from allies.

Solar Flare
Leona calls down a beam of solar energy, dealing damage to enemies in area. Enemies in center of the area are stunned, while enemies on the outside are slowed.
Incredible skill that has a long range. You just have to be careful because it's easy to miss the target. This is a great ability to use on champs that have AoE ulti like Katarina or Annie.

Like it was said in the beginning i play Leona as a tank. I don't buy any items that have AP or anything else.
For me it's just waste of money, furthermore you are the one who has to give your teammates possibility to get kills. Being a tank is not to go after frags, it's to make your team opportunity to go into a teamfight and make sure they will be alive and enemies will be dead.
To be honest you don't need any damage to win the game. You need to be near your allies, protect them when needed and be as unkillable as it is possible. To do this you don't need Trinity Force. At least i don't need it.

Exhaust&Flash
I always take Exhaust and Flash, because sometimes my slow and stun is just not enough.
You use your stun or ulti but someone is still running away? You can use Flash and Exhaust, activate shield and stun him again or use Zenith Blade. Now he won't get away!
Exhaust is useful also when you are ganked and there is a small chance you will run away being in bush. You see that they are after you teammate? Use Flash and Exhaust on one of them and if you can stun another or just start to autoattack. Make sure that someone, who is with you gets away. We don't want our AD carry or AP get killed!

Other Summoner Spells that you can use are :
Teleport
It's nice when your tower is targeted, everyone is somewhere else and you just teleport there and save the tower or when everyone is there and the only thing they need is you.

Ghost
Instead of Exhaust you can take this spell to chase your enemy and get him stunned/slowed. Yet be sure that your teammates is right after you to take the kill. You can also take this to increase your chance to escape from death.

Ignite
Take this spell ONLY in situation when no one is able to get it. Usually there is no need, but you never know! It sucks when Swain or Tryndamere are healing like hell on teamfight and you can't do anything about it.

I like my 9/21/0 masteries because they give quite good amount of life and regeneration.
It's also ok if you take any other masteries like 0/9/21 or 0/21/9.
It really doesn't matter that much.

As you can see my runes are mostly two types.

Quintessence of Warding and Greater Mark of Warding for Magic Resist

Greater Seal of Resilience and Greater Glyph of Resilience for Armor

Additionaly i have Greater Quintessence of Swifting to make her move a little bit faster. If you want you can buy whole set of it. It depends if you want more armor or to be really fast.
Now,why not Mana Regeneration or Cooldown Reduction or Heath?
On level one when I buy Doran's Shield i have 685 HP, about 62 Armor and 54 Magic Resist.These are really good numbers. After casting my shield I gain 92 Armor and 84 Magic Resist. Now, this is much better! You won't have any problems laning against someone that has 15-20 AP or meele champs. Of course that doesn't mean they can't kill you. They can. But it's not that easy when you have that amount of Armor and MR.
It's true that Leona is very mana dependent, but if you use your skills only when needed there won't be any problem with mana. If you feel like it's not enough then go to town and buy one or two mana potions.
What is with Movement Speed Rune?
Well, I was so irritated that Leona was so slow that it was driving me crazy. When I was in town and my allied were attacked i was just saying 'Faster, faster' and of course she didin't listen, so i bought this rune and now i feel better =]
So in my opinion, there is no point in buying any other runes, because you will be able to protect your lane for a long time playing safely and wisely.

Let's talk about my item build :

I buy this item first. When I bought Leona I used to start with Regrowth Pendant and Health Potion You can do that if you want, but i prefer Doran's because except health it gives also armor and health regeneration.
I noticed that when Leona is below half of her health and stays away from enemies her health regeneration is also good with Doran's. You can just go around minions and your allie and after short time your health is almost full.

First thing you do after going into town is to buy shoes. I know that you all know it but being behind your teammates is not funny at all. You can also buy Mana Potion . I like to buy it because when i go and attack someone i spam my skills and when enemy is low health i don't have mana to stun/slow him and neither my teammate has. I also take it when I'm alone under tower and a wave of minion is coming. Activate shield, scare enemies away and kill'em all.

Usually when I go first time to town i have money for Belt and for Boots. This way I don't have to go back twice. It's good item for early game because you already have a decent amount of Armor and Magic Resist. Especially when you are laning against Range AD or AP and they are harassing you all the time.

It's time for some Magic Resist. I often buy this item after health, even when i have on my lane AD champ. Why? Because it's the moment when ganks are starting. I wanna make sure that when AP champ will be on my lane I have enough MR to counter him.
If you have really big problem with AD carry don't hesitate and buy some more Armor and then Magic Resist.

This item gives you good amount of Armor. Now with your shield on you should have about 170 Armor. I usually have it around level 8-9 I guess (don't wanna lie).
Now there are two ways to get another items. If you see that enemy AD carry is getting feed and they have problems to kill him buy Cloth Armor and go with Thornmail You can hope that enemy will kill himself :D.
And the other thing is...

The beloved Sunfire Cape. Except of Health we have Armor and we deal magic damage all the time. That's why i like to buy it!

I know. Boots are before Sunfire Cape. It would be the best when you go to town and already have money to buy Sunfire and Boots. If don't , thats no problem.
These shoes+negatron+shield ahould give you about 180 Magic Resist. I like having much of it because i hate countering AP champs, especially Lux or Le Blanc
They have insane ulties and we must make sure that when they go with it we won't run away to the base first.

More an more Magic Resist to survive and kill them :). It's a lot easier to make Force of Nature when you already have Negatron Cloak. We bought it in early game.

I just love this item. It's perfect for AD champs that are annoying you with harass or are just hard to kill. Now you have gain 100 Armor and with your Shield and Sunfire and Runes you have around 300 Armor.

More armor?? Why not, as a tank you have to be resistant to any incoming damage in teamfight.
You also get Cooldown Reduction which is great. Spam skills as often as you can.

The last item i wanna get is Banshee. To tell you the truth I bought this only few times and the game was really long. Another amount of Magic Resist. You also get health and mana. And what's more important if you go for a team fight you have double shield double shield :)
Other possible item purchase:










This is for those who are laning against good AD champs. You can see that Thornmail is the first full item to buy. We have less Magic Resist but that doesn't mean we are more vulnerable to them. If you want you can buy Guardian Angel after Force of Nature. It gives Armor and Magic Resist and revives you after death. You have a chance to escape.











Here we have Warmog's Armor in first place. If you like having lot of life this item is suitable. We also have regeneration and life from killing minions. The rest is pretty much the same. Again if you feel that you have not enough MR and Armor you can buy Guardian Angel.

This chapter is about Leona playing in a team. I will tell you about my Skill Sequence, what I do in lane and team fights an why I don't always chase champs with low health.
EARLY GAME
The game start, I have level one, buy Doran's Shield. 62 Armor, 54 Magic Resist. Where do I go?
If you have support in your team, don't ever go with him (don't laugh I played like that). Someone is saying 'I won't go with tank because we are premade'. So what? If I go with Soraka there is no damage, no kills no nothing.
So you wanna go with AD or AP champs. It doesn't matter if his range or meele. He has damage and you wanna feed him with kills. On level 1 i try to scare my enemies a little bit so I start with my shield. I go over their minions, activate it, wait untill it explodes and run away. If i'm getting hit and see that i can't do that I just stay close to my allie and make him farm minions. This is very important. You want him to farm almost all the time.
Yes, you can kill minions too :P, but be sure that both of you get last hit.
Now I wait for level 3 to have stun,shield and my dashing sword. It's time to strike. Don't do it under tower, unless you are sure your teammate gets the kill. The best option is to strike in the middle of the lane, when they don't expect attack. Use Zenith Blade first then Eclipse and Shield of Daybreak to stun. I also use Exhaust if the enemy is escaping. If they escaped don't panic. Go to town buy some items go back and do it again.
I gain level 6, so what? Now i wait for the moment when I can cast it on someone so he gets stun and his allie gets slowed. So, you cast Solar Flare, activate Eclipse, dash to enemy with Zenith Blade. In time when you dash to enemy, your shield should explode and slow them one more time. And don't forget to stun with Shield of Daybreak.
Now your teammate should get kill or even two. He didin't?? Well, the enemy must be really lucky or really good at escaping or your allie has low reflex =]
Was there something about Skill Sequence?
Indeed, as you can see i max Eclipse first. On level 6 without any armor items I have more than 100 Armor when i activate it. You can protect and scare in the same time. I love using shield when enemies are about to attack my teammate. When it explodes they receive damage and go back.
Second I max Shield of Daybreak. Stun,stun and one more time stun. Never enough of it. And enemy team will be freaking out.
The last is Zenith Blade. I use only for getting to enemy and use other skills. And of course on level 6,11,16 i give point to ulti. Don't forget that.

MID GAME
Till now you should have at least Boots,Negatron and Sunfire Cape. Your teammate should also have some kills. If the enemy team has a ganker don't forget to buy wards. If they don't in mid game you should buy it to make sure that you won't be suprise by visit of mid champ.
In mid game I look on the map and watch if there is something going on. If yes then i go on mid or any other lane to help. My lane is being ganked? No worry, if I have ward i will fall back. They are four? Stay as close to the tower as possible. If they strike use your ulti and make your teammate get away somehow. You can use exhaust,flash, every skill, you can even die.
For me, one of the most important this in playing as a tank is to protect others. If you see that your tower is low, fall back as well. There is no point staying under it, when it will be destroyed anyway.
Ok,now one more thing. What to do when one of the enemies is low health and the other full. Of course you go and attack the first. Now he has go 150 HP, great let's kill him. Damn, the other one is after my laning allie. Do i go after frag or my allie? It's obvious that you want to protect your teammate! Yes,do that. Dash,stun,autoattack. Whatever you do to stop him. You shouldn't get killed if it's some squish.
Now we have team fight on mid. Everyone is standing there. Wait or strike? And you stay there like 10 minutes wondering. Don't. Watch which champion is close to you (except tank). If you have Ashe in team she will start the fight by throwing her arrow. Then you go first with shield. If you are surrounded by enemies go with ultimate. They all should be stunned.
Let your allies finish them. You are dead? Oh well, you did what you could for now.
If your team failed in team fight, it's good to think which champion deals to you the most damage. Buy items against him and focus other time.

LATE GAME
This should be the end. For my team of course. It will. With my items I should now be almost invincible. But it is not the most important. Late game is time when you go and hide,then strike,go back,hide again etc. You must be cautious. If you will get ganked,suprised,you might get a little bit stressed and miss ulti. Then there is low chance you will win team fight. Don't panic. Don't split. Where are your allies there is you. And don't allow anyone else to go first. Never! If he is, he is dead. When you go,there is a chance you will be focused in whole team fight.
If the enemy is splitting,stay together. Don't go after one,because the other will go behind and kill your allies. Go farm minions and when everyone is full HP you can go to break the tower or check the baron. It's sure thing they will be there. Go, ultimate, kill them and go for win!

There are also some tips that i wanted to write about the game:
1) Buy wards. This is very important in late game. It's good to know where enemy is.
2) If you have support in team, let him buy oracle for enemy wards. If not, buy it yourself.
3) Remember to go first in lane.
4) Don't be stressed when you have stats like 0/6. If you feeded your teammate he should be tankfull
5) This build is for enemy team that has 2AD+2AP+Tank. Notice that you item purchase is addicted to enemies strongest champ. (That's why i wrote some alternatives)
6) Always try to protect you allies.

This is the end of my build and i wanted to say that it's my first so please don't be so harsh on me :).
I hope that it will help someone to play not only Leona but also other tanky champions.
Also i wanted to thank a Summoner named Spoll, because of him i learned how to play Leona - The Radiant Dawn.