Hello, and welcome to my build on Leona, the Radiant Sun. Leona is a tanky champion who has an arsenal of crowd-control abilities at her disposal in order to destroy the enemy team.

For runes, I always take Greater Seal of Vitality, Greater Glyph of Scaling Magic Resist, and Greater Quintessence of Scaling Cooldown Reduction for sustainability and cdr on her skills. For the tanky dps build, I take Greater Mark of Magic Resist for even more sustainability. For the AP build, I take Greater Mark of Magic Penetration for her magic attacks.

For the tanky dps build, I take 1-21-8. 1 point in Exhaust helps add to your CC, 21 in defense helps with your tanking, and 4 points in Awareness helps you lvl faster.

For the Tanky DPS build, I start off with a Regrowth Pendant and a Health Potion in order to stay alive in the lane. When you have enough, quickly turn it into a Philosopher's Stone and a Heart of Gold for the gold/5 and added tankiness. Grab a Boots after you have enough and then start working your way towards your Trinity Force, grabbing the Phage first and then the Sheen . Turn your normal boots into a Ionian Boots of Lucidity for the CDR, and then turn your Heart of Goldinto a Randuin's Omen. Next off, get a Sunfire Aegis (haha sun) for the tankiness and magic dmg passive, and then get a Force of Nature for increased health regen and MR. Finally, turn your Philosopher's Stone into a Shurelya's Battlesong for CDR, health/mana regen and a movespeed effect.

For the AP build, start the same way as the Tank DPS build, but dont bother getting a Heart of Gold this time. Instead, after getting your Philosopher's Stone, quickly get Sheen and then the Ionian Boots of Lucidity. Next off, get an Abyssal Mask for the MR, AP and MR reduction aura, and then a Frozen Heart for its Armor, Mana and AS slow. Turn your Sheen into a Lich Bane for added dmg and MR, and then get a Zhonya's Hourglass for more armor and AP. Finally, get your Rylai's Crystal Scepter for more health, AP and a slow effect on your abilities.

Will of the Ancients: Good if you want more AP and has a spell vamp in it to help you stay alive.
Mercury's Treads: If the enemy team has a lot of CC, you can get this over your CDR boots.
Banshee's Veil: This can replace FoN and gives you some health/mana as well as a spell shield.
Frozen Mallet: If your aiming for more HP and some attack as well as the slow for chasing.
Guardian Angel: Good for its armor/MR and its revive ability.
Atma's Impaler: If you're stacking HP and want to dish out some damage.
Rod of Ages: If you want that tanky AP feel, this is good too.

I always start off taking a point into Shield of Daybreak for its stun ability, in case I get engaged on. At lvl 2, I take a point in Zenith Blade and at lvl 4 a point in Eclipse. I max Shield of Daybreak first for extra dmg and lower CD stun, followed by Eclipse and then Zenith Blade. I always get a point in Solar Flare whenever i can.

People have been debating this a lot on whether you should max Shield of Daybreak or Eclipse first on Leona. IMO, I think Shield of Daybreak takes more priority over maxing Eclipse first. Even though Eclipse gives you more AoE dmg/lvl as well as a larger armor/mr shield, it always stays at the same CD. As you lvl Shield of Daybreak, though, you get added dmg as well as a lower CD. With my CDR items/runes, it will go to a very low CD at lvl 5, which can and should be used on carries all the time. I feel that you are tanky enough not to max out Eclipse until second, and the passive still hits AoE if your shield does.

For summoners, I take Exhaust and Flash. Exhaust gives you even more CC to threathen enemies with, and Flash can be used to engage/escape.

Other Good Spells:
Ghost: can be replaced with Flash in order to catch up/run away from a battle.
Fortify: always good on a tank, if you want to save your towers.
Cleanse: good if you are getting too much CC thrown at you.
Heal: healing yourself adds to your tankiness.
Ignite: if the enemy team has some heals and your team doesn't have any Ignite.

Bad Spells:
Clarity: You shouldnt be having mana problems unless your randomly spamming your skills everywhere.
Clairvoyance: Unless you're really good with this spell, it's a waste.
Revive: Try not to die.
Smite: This is not a jungling build on leona.
Teleport: You really don't need to be moving around on the map as much with this spell. You should be with your team at all costs anyway.
Rally: not very useful in most situations anyway.

People are also debating on where Leona should start off the game, either in the jungle, soloing top lane or with another person bottom lane. IMO, Jungle Leona is not very efficient (wayyyyy too slow, her Eclipse only does a minimal amount of AoE dmg and her passive doesnt work alone), soloing top is also not very efficient (Passive is useless and Leona's harass doesnt do much dmg). She's better at bot lane with a carry or someone who does much dmg (CC a squishy down bot and trigger her passive multiple times for your carry; gets you kills)

Pros:
Very tanky
Lots of CC
AoE CC ultimate
Can use ultimate when stunned! :)
Eclipse can last for up to 6 seconds as well as deal dmg
Sunlight does much dmg when teammates hit
Sunlight synergizes with AoE on W and ultimate.
Zenith Blade can get you right into an enemy team and targeting a carry.
Shield of Daybreak refreshes Auto Attack Timer and can also target structues.
Shield of Daybreak+ Solar Flare on enemy carry can stun-lock.
Hawt.

Cons:
Shield of Daybreak is semi-high CD
Zenith Blade is hard to aim, short distance plus you may not port to a carry
If Eclipse does not hit a target, shield only lasts for 3 seconds.
Solar Flare only stuns one person in the middle of it.
Sunlight can only be triggered by a teammate, not by Leona.

When a teamfight engages, you always want to be the first one to go in. Always pop your Eclipse before going in though, because you may die fast if its not on. Once it's on, try to wait 1 second before going in with your Zenith Blade, and then Using your Shield of Daybreak on the enemy carry. Then, Eclipse will pop and your passive will be on most, if not the entire, enemy team. Your team then attacks and triggers Sunlight, dealing much dmg. Use your Solar Flare on the enemy as well, aiming for the part where they are most clustered up. It is even preferred that you use it on the enemy carry that you used Shield of Daybreak on so that they will die faster and be stun locked.

Hope you like this build. guys! Comment on it and tell me what I can improve on, etc. Enjoy!