Singed descended from a long line of Zaun's revered chemists. Even in his youth, his talent for concocting potions far outstripped that of his peers, and he quickly distinguished himself from his less extraordinary chemist compatriots. It came as no surprise to anyone when he was selected for apprenticeship by the infamous Warwick, master apothecary on a lucrative retainer with the Noxian military during their campaign against Ionia. Within Warwick's laboratories, Singed toiled without end, rapidly absorbing every detail of his predecessor's deadly craft. Singed had little concern for the death and destruction that was the fruit of his labors. By the time the curse of lycanthropy descended to claim his master, Singed was poised and eager to make the transition from workhorse to innovator; he was ready to share his genius by bringing a new brand of suffering to the Ionian front. His zeal for progress was unquenchable, and when suitable test subjects proved to be in short supply, the eager chemist was often thought to turn his volatile mixtures on his own flesh.
When the uneasy peace created by the League of Legends settled on the world, Singed journeyed to the one place where he was still able to showcase his beloved craft: the Institute of War. By this time he was barely even a man, his body both ruined and sustained by his ingenious craft. A thousand burns - accidents of shadow and flame - mar his ravaged form, and exposure to such harsh conditions has deadened his nerves, hardened his body, and strengthened his physique, transforming him into a veritable juggernaut. This, combined with a formidable arsenal of deadly concoctions, make Singed a force to be reckoned with on the Fields of Justice.

Hi, my name is Tokushiro. Singed is one of my favorite champions in the game, and specifically my favorite tank. I like Singed because he is a great harasser and farmer. With this build, I usually get around 10 kills and 10-15 assists, if the game is long enough.

With Singed, I usually use Ghost and Heal.
I use ghost for obvious reasons, chasing or getting away. And combined with his ultimate, he can really pack a punch offensively.
Heal is for when you are low on health or your team mates are in team fights.
Alternatives
Exhaust: You can replace heal for exhaust. This really comes in handy when you are chasing and wanting to fling someone back.

Core Items

Rod of Ages: THIS IS A MUST HAVE FOR ANY GAME FOR SINGED. It builds your ability power, health, and mana. Its passive is also very useful.
Boots of Swiftness: Singed needs to be fast, so these boots are great.
Banshee's Veil: With Banshee's Veil, your health and mana increases. This is a tank build for Singed, so you need the magic resist. Passive is also very useful.
Rabadon's Cap: This is probably one of the last items you will get if the game is long enough. This is a great item for Singed, since his Poison Trail and Fling require AP.

Secondary Items

Guardian's Angel: I use this item because I like to get away, and I most likely do because of ghost or Insanity Potion. Also a great tank item.
Sunfire Cap: Excellent tanking item, and works good with farming/harassing.

Alternatives

Mercury's Treads: If you are looking for boots that actually have an effect, then get these. Singed will need to extra magic resistence.
Force of Nature: I really don't use this for Singed, but it is really good for tanking. The magic resistence, health regen., and movement speed can be very useful.

Early Game
In early game, you should take top or bottom lane (I recommend laning with a ranged-dps or mage.) You should max out poison trail first because it is a great harassing/farming ability. Early game is where you should get the Boots of Swiftness.

Middle Game
Now you should start maxing fling, you should have Rod of Ages, and you should start ganking. Make sure to participate in team fights to throw enemies back to your team mates. Now you should be saving up for a Banshee's Veil and Rylai's Scepter.

Late Game
You should now be saving for Rabadon's Cap. Late game is probably the best time for you. Now you can push and earn many assists. And your team needs you to initiate since you are a tank, don't forget that.

PROS:
Great harraser/farmer,
Tanking capability,
POISON!,
Great abilities,
FAST!
Can 1v1 anyone if built correctly.

CONS:
Not so good early game,
and can steal kills XD

Like I have said before, when picking Singed, be sure to use Adhesive and Fling A LOT! You need to slow enemies down for your team mates, and you need to assist them with Fling! Try to be in all team fights!

This is my first build :)
So at the end, Singed really is a great champion. Some hate him, some love him. I personally think he is one of the best champions in the game. If there is a Singed on your team and they are good with him, chances are you will probably win the match! I guarantee that this build will help you! I will be posting my match history with him soon!

P.S. Always remember that Singed is a support, but he can also be a carry. Always keep that in mind.