HI!!! my in game name is Jok3rz R W1ld and im going to tell you how I play swain.

Now days when I do run across a swain, im not really impressed, as many go as much ap as possible which i find to be a waste. Clearly not taking advantage of what swain is awsome for.
Simply put...tank mage. This monster of a champ is the master of master tank mages...not a pure ap champ imo.
The way i prefer to play swain is to cast my spell combos and deal my damage, as well as being able to push threw enemy lines and minions with my ult staying alive. Countless times over and over you can push threw these lines, make a kill or 2 and get out nearly full health.
SO....LETS FIGURE OUT HOW THIS IS POSSIBLE !!!

runes are simple <<< all magic pen Marks, and AP Seals, Glyph and Quintessences >>> with these runes and mastery set up, ull have a nice even damage at lvl 1 of 80+22 (102) on ur aoe snare or 75+25 (100) damage on ur dot.

Masteries are set up to get as much potential for this play style as possible... Increased armor of both types, ap bonus, health and health/mana regen and nice mana surplus. with ur starting item and 2 , you will have 511 hp, and 506 mana, a nice start :)

item build for this i know may seem unusual, but highly effecitve...keep in mind ur play style ideals around being a caster with ability to heal (not to rage threw people by running stupidly around with ur ult on..as it being hardly possible/effective anyhow.) concentrate on farming minions and keeping enemy zoned out of last hit range, and do it comftorbly!!

my item build order for this is once u reach roughly 2200 gold i port back and grab my and upgrade to and return to lane or gank if i see the need. try to remain farming minions as constant as possible as with ur ult and u can farm non stop and stay full life. when uve reached enough gold purchase then work toward the gold to finish a this will give u a decent movement speed, great health regen and nice magic resist. you next item will be which ull use to create as soon as possible. this is key to have, as well as ur next finished item...start ur next item with followed by and finish them to a this item will be ur secret weapon i assure you. when in a tight situation, replenish ur mana if low with , then activate ur ult and and watch ur life climb so fast!! but your not done yet... remember that little we have sitting around ? well by now it should be nearly maxed out with mana bonus so lets upgrade it to and our final item will be non other than that sexy which will shoot ur ap up by alot, giveing you 200+ damage from ur ult...meaning with that, and your easily 350 hp a sec.

as for summoner spells i wouldnt recommend anything other than and they just shine to swain like nothing else can

just wanted to point out that ur armor and magic resist at 18 will be 140 armor and 142 magic resist, not sure why its wrong on here...

To sum this all up...ive had a great experiance with this build and set up, i hope you give in and steer away from the pure ap swain, ull be amazed at the survivability and dominating aspect of swain i assure you :) GL and GGs fellow gamers !!!!