This is my first build. I came up with this build when I looked at Leonas passive. The passive doesnt makes it so your teammates do more damage when you spells hits an enemy and that makes it very difficult for Leona to get kills or farm. That is why I added a mejai because if you play her good you will get alot of assists and eventually full stacks.

For runes I picked much armor and magic resist because you want to have lots of surviveability throughout the game. At the same time I chose to get a little ap and magic penetration on the way to deal just a little more damage.

For masteries what you want to pick is lots of utility and defence. This makes you survive longer to stay in the lane and help your laning partner. It also gives you more gold for assists and kills which is perfect for this build.

okay this is the fun part! You want to start of with health regeneration to help you survive for a while until you get enough gold to buy Philisofer's stone and boots of speed, at this time you may also buy a ward and maybe a health potion. After that you should stay in the lane until you can afford a mejai, remember you want this as early as you can because from now on we are just going to build tanky so that the stacks we get on the mejai will last throughout the game. After the mejai you want to buy Mercury treads (Ninja Tabis can be an option if the other team has lots of ad) and Shurelia's Reverie. Shurelia's Reverie will help your team a lot when there are ganks on the way (It will boost you chances of getting kills in fights) and it will secure you an assist for a stack at the mejai's. After the Shurelia's you want to get more and more defence for even more survivability and what I usually do here is buy a Negatron Cloak but you can buy a Chain Vest before that if the other team has more AD. After that you get a Guardian Angel to make sure that you wont loose your stacks. Now we have pretty much defense so we can go ahead and buy a little more AP and completing the Abyssal Scepter. The final item is really your own choice I usually go Thornmail to keep the AD carry of me (and at the same time deal lots of damage if the ad carry focuses you). Some other choices are Sunfire Cape, Randuin's Omen, Force of Nature or Banshee's Veil.

For Skill Sequence what you do is start with the stun (Q) and your E at lvl 2. From lvl 3 and up you max your W because it does great damage and gives you a lot of armor and magic resist.

On summoner spells I usually go with Clairvoyance and flash. The Clairvoyance can be swapped with heal if you dont play full support and want to have more sustainability. I use the flash to get in my stuns on the enemy or to flee when low on health.

To summorize this build is to get mejai's fast and get as much assists or kills as you can ( always go with your team for possible assists/kills) and then build up your defence so you wont loose your stacks. This guide has worked very good for me so far ive gotten 20 stacks almost every game and have carried my team to victory! Good Luck Have Fun using this build!