Hi there viewers of this guide, this is my first guide on this website and I felt like putting out one of my own for Leona. I have been playing Leona during her free week and felt I found a decent enough build for her that I would like to share. I do not think of myself as the best player but I have my moments. I tend to main with Heimerdinger since he is indeed one of my favorite champs out there and was the first champ for me to play. Leona is a very fun champ to play as and is the most fun I can have playing as a tank champ since I tend to lead towards more ap variety of champs for the explosive factor they usually have! =D With no further introduction...

I call this the 3 Click Build because at the end of building your gear you end up with 3 clickable items at your disposal!

I chose the masteries like this because I felt she is a tank so of course she should go down the tree meant for tanks but also down the offensive tree so that she can get as much cooldown reduction as she can since her abilities tend to have a huge cooldown. Getting the cooldown on them much lower really helps her out. At the end of investing mastery points you have one point you can stick in improved ignite or improved ghost run or perhaps in Dominion improved promote!
Good amount of variation you can use.

I like to put one point into each skill while leveling up just so she has the basics of being able to reach her target with Zenith Blade, stunning them with Shield of Daybreak and dropping Eclipse on top of their head.
I like to level up Eclipse first because having that extra armor and magic resist is what is going to make you much more tanky. 70 extra to both at lvl 5 eclipse. Makes it a swell deal wouldn't you think?

I find these summoner spells to have uses on Leona-

Flash- Good for popping out of reach from a foe or jumping on them and dropping eclipse.

Ghost- Same as flash, another opener or tool to run away with.

Ignite- Leona has a good deal of burst and dropping this on them is a handy tool to have.

Exhaust- Another slow is always handy.

Teleport- This has its uses for teleporting to safety in the midst of being chased or for teleporting on a turret to attempt protecting it.

Some Summoner Spells that have some use that can also be used-
Fortify
Clairvoyance
Heal
Cleanse
Revive

These can be used at lower levels perhaps or if you feel like mixing it up. Clairvoyance(CV as some people say) can be incredibly useful and a game changer. It can help detect ganks or used as a way to scout bushes and try finding enemy champs if they are MIA(missing in action).

Heal is good at lower levels because heals are always nice and can sometimes change the tide of battle in a group fight if the going is close.

Fortify is awesome if you choose to grab the fortify talent in the defensive tree. It adds a lot of damage on the turret and if you are being turret dived can really put a dent in their attempt and deal some good damage with the splash from the reinforce.

Cleanse has it's uses, I tend to not use it, but if you feel you want more control over being controlled then this spell is for you!

Revive can help at the end if your group dies and they are rushing your base. The cooldown on it is very long though and I tend to not like it.

Some summoner spells to avoid would be

Clarity
Rally
Smite

The reason I say no need for clarity is yes you do indeed have early mana problems. But as you lvl up your mana bar eventually becomes no problem at all.

The items I chose specifically try to buff her offense and defense, her defense is buffed through a little added health along with very good armor and magic resist.

I grab the gold per 5 items early on to maximize their effectiveness and grant as much gold as I can possibly get from them. I usually start with Ruby Crystal just to start her tanky right off the bat but may also grab Regrowth Pendent if you feel the need for health regen, this also can build towards your Force of Nature.

Once I retrieve my gold items I build Ionian Boots of Lucidity. The CD reduction is very handy to have. I would finish up the Force of Nature for the magic resist and added health regen or grab a Chain Vest in case of a heavy melee team.

Once you have all of these built, it becomes time to build up a small amount of offensive power. Starting with Rod of Ages and Zhonyas Hourglass. Grabbing these further boosts your health,mana, armor, and ability power along with the cool clicky from Zhonyas.

Finally once you build these you can build your Deathfire Grasp from your Lucky Pick for an additional 15% cd reduction and another clicky ability to drop a decent nuke on a full health enemy, and Randuins Omen for a 3rd clicky item which grants an effect like an aoe exhaust but will last much longer with your high armor and magic resist.

A good note would be that if you want you can switch out force of nature if there aren't many magic users on the opponent team and switch to Warmogs for extra health or if you want a little bit of magic resist with armor can grab guardian angel.

Pros:

Okay Armor and Magic Resist.
Wide array of clickies at your disposal: (Nuke, Immunity, Aoe Slow)
Decent enough damage.

Cons:

Not as much health as tanks who build for health.
Early Mana Problems

Don't mind the Annie win there. I do pretty good with this build, sometimes average but overall okay. The main thing is that a lot of the games I never got to build my full build. Your Ultimate is a lot more effective with more ability power since it has a good AP ratio on it. Perhaps a full out AP build would be interesting to see. Either way I find this build fun and does a good job with making Leona deal damage while still being able to tank. Somewhat =)