Leona is freaking flexible.

This champs kit is so dang flexible, you can literally do anything with her.

You can go top. Mid.(as a Assassin counterpick) Jungle. All successfully(Granted you don't counterpick yourself into oblivion.).

You can build her as a Fighter, as a Tank, as a AD assassin, as a AP assassin. All successfully. You can go Thunderlords, Fervor, CoC, all successfully, depending on what your matchup calls for.

Her dueling power is sky high. Her jungle clear with a standard 8.5AD 17% AS page is 1.2seconds slower than a Leesins full clear. Her ganks are dangerous as hell. Her counterganks are dangerous as hell.

Her downsides, The only way youre really going to escape a gank is to Zenith Blade+Q into the enemy jungler, which depending on what champ that jungler is, may just get you killed regardless. Her lane clear is pretty bad, feels extremely similar to playing Pantheon in lane. Your dominant over your opponent, at risk of being ganked, and your lane shove is craptastic.

Sorc Boots(or tank boots if the matchup calls for it) Hextech Gunblade Trinity/Lichbane/Gauntlet Knights Vow Spirit Visage Last item, whatever you need.