This is my first build, but it works great for me, and hopefully it will work great for you as well. I get 21/9/0 masteries, for increased damage, and my runes are also meant for the same principal. The items I chose are so you have a lot of survivability, as well as an increase in damage even with your Q, and ult abilities. Now just because I say that you will have more survivability, doesn't mean you are invincible by any means, all I'm saying is that it is a lot harder to kill you. If I forget to mention anything, or you would like more information, please say so and I will answer your comment as soon as possible. Alright, with that being said, let's get started.

I pick Ghost, and Exhaust, so you can catch up to/ run away from enemies. If you prefer flash over ghost, be my guest. But your Demacian Standard/Dragon Strike combo works as a flash, and you can knock enemies in the air while doing it to disrupt them as you make your escape, or your set up to engage. Don't get clarity/heal, Shurelya's Reverie takes care of your regeneration. no need to waste a summoner spell on those.I've never been a fan of taking clairvoyance, or fortify but if you like them, go ahead and take one. Teleport, rally, ignite, and cleanse may be used as well, but I personally prefer not to take those with this champion due to the increased survivability/damage you can do. You're not jungling, so don't take smite. And I hope to god you don't even consider taking revive. If you do I will laugh in your face.

For the items, The reason I get Shurelya's Reverie first is for the health/5 and mana/5. after this item you shouldn't have that bad of mana problems, unless you are spamming your skills. Another benefit of this is that you get that cool down reduction, as well as an amazing active for escaping/engaging with your whole team (if they're close enough to you.) Sunfire cape is great for that little bit of extra damage that you put out while in your wonderful crater you create with your ult, and it also gives a decent amount of armor, and a boost in health. Force of Nature, I only get this if there is a threatening caster on the opposing team, such as Karthus, Anivia, Ryze, etc. If there is not, go with Thornmail. Thornmail gives you a lot of armor, and it's passive is amazing against champions such as Master Yi, Tryndamere, etc. Warmog's Armor is for that huge boost in health, making you harder to kill, and giving you some more attack damage for when you get Atma's Impaler, which I will talk about in a bit. Frozen Mallet should be self explanatory, but for the sake of talking, I'll tell you about it. It gives you more health, more attack damage, and gives you an amazing passive for chasing down those annoyingly quick champions. Finally, Atma's Impaler, this item gives you even more armor, a decent amount of crit chance, and the passive attack damage based on your total health (2% of your total health is added to your attack damage). If you don't want to get Atma's Impaler, you may get Guardian Angel instead, for more armor, magic resistance, and a nice passive if you get greedy and die a lot. But I prefer Atma's Impaler just because you can kill people so much quicker due to the passive on it. :)