So, I've been playing Leona lately...
... in the jungle.
Edit: UPDATED AGAIN AGAIN
Runes; AS Marks, Armor Seals, MR Glyphs, and AS Quints.
Masteries: 9 / 21 / 0
(Still trying out 0 / 16 / 14, but first impressions are that it is simply weaker with the below build)
Items:
Core; 
Boots; 
Offensive; 
Defensive; 
With the core, you get damage and tankiness all in one go. Devourer let's you farm and fight. Wit's End multiplies Devourer and gives MR. Iceborn Gauntlet gives literally every stat you could want and a passive that makes clearing faster and CC-ing better. Of the boots, I tend to just go with the flow. No matter what you're picking up from the offensive group, you're just getting a lot more damage while still acquiring survivability. Within the defensive group, these are reactionary buys for surviving against certain targets.
Start off with [Q], have a hard, smiteless leash on Red/Blu (whichever is nearest to bot). Level [W] next. Don't forget to say "ty" for the (hopefully adequate) leash. Proceed immediately to Gromp and use your potions. Smite Gromp at the start, after you kill it, take your next buff. You should have little over 1/3rd health left, but this is plenty to gank with. Take a Scuttler if you need even more health. After your first back, you should have enough gold for Sabre, boots, and pots. Gank whenever you can, your focus is getting gold for Devourer. Farm, gank whenever an opportunity presents itself, and don't forget about Dragon. Or the Scuttlers. Don't be afraid to buy pots afterwards, if a gank goes bad or you fall behind in level, you're going to need them.
Micro-Farming Tips: [Q] is an AA-reset. Use your stun just before the largest creep attacks so it doesn't connect. Use [W] just before being hit by the large creep to maximize the time with your armour. Don't use [E] while farming. It just wastes mana and time. Attack the big creep every other time early on, to optimize the DoT from the Jungler passive and Red. Focus on stunning the big creep with Heavy Hands. Don't overlap it with [Q]'s stun. Smite Gromp just before it attacks you to maximize time using the Toadstool Armour.
The only problems I've discovered thus far is that they need to prevent you both ganking and farming to make you less of a threat. Later on, slippery champs will pose the most threat to you, since it's harder to lock them down. Whatever you do, don't waste your ultimate trying to start a CC-combo. Between End and Gauntlet, pick up whichever resistance you need first, both build paths provide you damage anyways. You're so tanky that you have what feels like all the time in the world to hack away at your target with a damage steroid that scales as you farm. I've gotten double kills like nothing with this setup, and they can't do a thing about it once they're caught.
Author's Notes: I'd consider a good leash to be when they leave it at ≈200 health. I've thought about Nashor's Tooth and Rod of Ages, but I haven't tried them yet, nor do I think I ever will. I chose Sabre because of the wonderful fighting capability it provides. You don't really need the sustain from Trailblazer, nor the CC from Stalker. Yes, I tried Thresh, too. He isn't tanky enough to survive, and overall feels weak during the early game. It's also hard to collect souls while you're in the jungle. Maybe I just didn't kite the monsters nor leeched off of lanes enough, but that's my first impression.
Thank you for reading.
early if going for 
Face of the Mountain is 91.3% gold efficient without the passive and active effects. (source: lolwiki)
+ tank. Start Q and win all the lvl 1 trades
or 
, I've jungled leona every now and then before the jungle change and I've always built her tank. I wouldn't bother with the 
> 
, I lose out on flashing over walls and such but 
Core 
Situational Tanky: 
jungle? Hes what I play jungle wise, and he has very nice sustain with his Q and W, and once he builds his