This is my first guide on here so if you want feedback comment me and don`t downvote me without letting me know why or because you have a guide you want to promote.

Swain is an ap carry that usually is in the midst of the fight, and because of that he has intense sustain with his ult and is considered to be one of the better ap off tanks because of his immense crowd control

Pros:
Great single target Burst
Fairly tanky
-His e Give you a percentage more damage with your other spells and basic attacks
-his passive is great for laning, mixed with the new dorans you probably wont go back until late game
-Not alot of health problems when laning after level 6
-Unholy grail and blue buff make you a god
-Great survivability
-His ult heals while you are hourglassed

Cons:
-Ignite hurts alot
-mana problems if you don`t conserve
-ult and w are the only multi hit spells
-your q can be cancelled by walking away from it
-fairly slow

For swain I usually get a dorans first, but if u have to dodge skill shots get boots and health pots.

Next i go for ether Liandry's Torment or Rod of ages, depending on how the game is going

I finish my boots next get Liandry's Torment if I grabbed the Rod of Ages first or Ryli's if I already have it to mix in a slow and to improve the damage of Liandry's Torment

If I find Im being picked on by ad or if I just need survivability I get Hourglass, If I`m doing well I get Deathcap`

When I find I need more mana I get Unholy Grail or Archangle's Staff depending on how many kills I get in a fight or if I need the defensive sheild

Doran`s Ring : Great starter weapon, alot of ap mana regen and some health

Sorcerer`s Shoes : Great early magic pen, Brings you closer to true damage

Liandry's Torment: Health magic pen ap and a dot that reaps havoc in team fights

Athene`s Unholy Grail : Used to be Swain`s god item, But since the ap nerf I have strayed from the item or bought it last but it has lots of mana some mr and a tone of regen mix in blue buff and your ult will last all day

Rod of Ages : Great mix of survivability and damage plus the mana helps with your ult

Rabadon`s Deathcap : A great item for ever ap user

Zhonya`s HourGlass : 100 ap plus the active and armor give it the second most viable ap item and best survivability item in the game, when the team targets you ult and use this and your golden. If your in your ult when it goes off it will heal you.

Abysal Scepter : good ap and mr plus it gives the other team a debuff, great for when the enemy has low mr

Void Staff: good ap and ok magic pen, get this for an mr heavy team, since Liandry's Torment stacks with boots you don't really need it.

Rylia`s Crystal Scepter : If I find I`m not having health issues or if I`m dealing with a fast team I usually switch Rod of ages out with this, otherwise I don`t get it, the slow is nice but you already have a slow with your q and your w roots.

It does work well with your ult and Liandry's Torment.

Will of the Ancients : I don`t usually get this because you will usually get ignited, and more ap = more damage which mean more health from your ult, but if you have a support or someone else who can grab it strongly encourage them to since its a nice help to you and your team.

Deathfire Grasp: Great item, if i`m doing well sometimes i will get it if i`m facing a team with alot of hp or if I need to burn someone down fast, It works well wit Sawins e and I tihnk it stacks so you will do 40% damage to peaople

I get the Basic Damage masteries from the offence tree and mana regen, mana.
Runic infinity is good if your jungler doesn't need blue but If they do get 1 level in greed

Focus on farming and if the other Champ gets near you hit them with an e then q.
Save your w for when a champ is running away and guarantee you a kill or for escaping.
Ask your jungler for blue, it will help alot at level 6.
Use your ult to heal from damage, if you stick near there minions you will be hard to kill

By now your should be fairly tanky and be able to take some damage as well as deal some. Slow the squichies with your e q combo and keep bird forum up for as long as you can, remember it has a cooldown and when it is down is when people will attack you so try and duck out of the fight for a few seconds if you have to cancel it or if you are low on mana

Thank you for reading my guide, if you have any comments questions or anything else feel free to post them, I will try to answer all of them