Leona Top
Tired of yasuo top? Want to humiliate the shit out of him and probably make him rage quit? i present to you,
Top. (I know darius is a counter but leona is way funnier cause his team will probably flame him for feeding support top lol)
First Buy
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/ Or
If snowballing, the sheen proc is really nice on leona's Q. buy iceborn if you are loosing lane and just wanna be tanky.After you Finish your Cleaver or Triforce you should finish
.
If snowballing rush
OR
(Frozen mallet is fucking hilarious and i get if even if im not snowballing lol)
After you finish your core items, go tanky. All tank items work depending on the comp they have but i rush
if i want to push the lane in. If you want 40 Percent CDR, Get
But Generally you might want to rush 
Masteries: 18/0/12, You want fevor to do damage and the extra health and summoner spell cooldowns to help your team. Take flash Teleport.
Runes: AD Reds, Armor Yellows, Cooldown Blues. Self Explanatory.
Leona top is actually really good, she can lock down her opponent with her Q and E so the jungler can gank and she can also use Q to escape. She has GREAT roam potential and her presence can cause the mid laner to flash after she uses E.
and then go into the rest of your build. Aside from that, the rest of this post is correct and accurate. As soon as she has bami's the lane is auto won. So basically at minute 6 or so.