When I came home from holiday the other day, I went straight the the shop and bought Leona.
I am so fond of tanking, and all my friends had been texting me over the phone how great she was, and I just had to get her. It was love on first sight (or spellcast, whatever sounds better)
My first game ended with the fine score of 7-2-17.

I want to thank Riot for finally making such a thrilling and balanced champion. Now you have proved you are capable of making good champions.

My intention was just to make a build, but there is a few things I want to explain about it as well, so you should consider this a short guide to how to tank with Leona.
And yes, it might be similar to other Leona builds (I have not bothered checking a lot of Leona builds, as I figured her out by myself pretty fast), but I assure you, this is not some copy paste from someone else.

I am open for constructive critism and/or praise, trolls and unserious comments will be ignored.

Runes:
Marks: Magic penetration. Because you want your spells to deal as much damage as possible.
Seals: Dodge. I have always been very fond of dodge runes. They are not as "safe" as armor runes, but there is so few dodge items in the game, and so many armor items. Thus I pick dodge runes as this is one of the few places where you can get it.
Glyphs: Magic resistance. Spellcasters are always a pain in the *** early and mid game. Lots of early magic resist early will counter those pesky nukers.
Quintessences: Magic resistance. Same reason as above.

Masteries:
Pretty much standard defensive masteries. The thing I do different from many other players, is that I use my remaining 9 points in the offensive three to increase my damage some more.

Summoner spells:
Summoner spells is only a matter of preferences. They all have their use, but Teleport and Flash is what I prefer the most.

Your item build will be different almost every game. It's very obvious why. But I would like to recommend some, as well as sharing my core build that I always use.

Core:
Boots
Philosopher's Stone
Heart of Gold
Frozen Heart
I always rush those items. You upgrade your boots when both the gold per 5 items are done. And rush a Frozen Heart (Don't do this if the enemy team got no AD carry)

Warmog's Armor
I highly recommend this item. Leona is incredibly tanky with Eclipse and thus you can afford to ditch some armor/magic resist for this item. And it's pretty easy to stack as well.

Leviathan
I actually encourage this item. Leona is so hard to kill, that you have a chance to get max stacks on this. And if you got stacks on it, it also forces the enemy team to kill you, as they don't want you to max it. Almost like a passive taunt.

Force of Nature
Incredible item, on top of all the magic resist and HP regen, you get movement speed that always comes in handy. HIGHLY RECOMMENDED!

Lich Bane
One of the last items I get. You should fetch a sheen in mid/late game, giving you more damage so the enemy team can't just ignore your presence. It also got some magic resistance which always come in handy. And with this you will be able to nuke the **** out of the enemy glass cannons.

Your gold per five items can either be upgraded or swapped out late game. Keep them as long as you have space for them.

Versus a well balanced team I would use these items:
Mercury Treads
Force of Nature
Warmog's Armor
Randuin's Omen
Frozen Heart]]
Lich Bane

Versus AD or Magic heavy teams it's really easy to to play as tank. As you will stack whatever resistance counter the team, and simply nuke the sheit out of the "outsider".

Let's make this short and simple:
Try to always activate Eclipse before engaging (Beware, this will alert you enemies, thus making it a bit tricky when harassing) it will make sure you don't die too fast.
Usual harass rotation is: W -> E -> Q. But sometimes you will have to wait with you Eclipse until you have stunned the opponent.

Be patient with your ultimate. You want to trap as many players as possible in it.
You should always be attacking the main target, as your passive will help you team to nuke them down faster (Means: Don't auto-attack tank).
With my build you should have enough CDR to spam your spells. Use them often. Especially your Eclipse Activate it as soon as it's ready when you are in a fight.

Thank you for using you time on my build/short guide. Hope you'll get many sucessfull games with it.