I didn't make this build but I think it's a great build that I have been destorying with the past few days, and I just wanted to share it because it seems like no one has posted it on Mobafire so far.

Recommended: "Teleport and Ghost"

These are summoner spells you want to take if you want to split push; because of the way you demolish waves of minions, you can usually get in a good push on lane before getting into a team-fight. Teleport also allows Singed to spend more time farming and less time traveling to team fights for objectives like Dragon, Baron Nashor, or a group push

Alternative: "Ignite and Ghost"

These are summoner spells that will get you a kill early. Ignite goes along great as a DoT (damage over time] with Poison Trail (Q). A good Fling (E) with your Poison Trail (Q) on plus Ignite will deal significant damage to an enemy. You want to take these summoners if you’re worried the enemy team’s heals will be a problem for your team (Soraka, Nidalee, etc).

Laning Phase: In the early laning phase, you want to focus on farming because Singed is not very powerful without items. Play passively, and don’t try to exchange hits with the enemy champion. You don’t want to lose health, you just want to safely make it to level 6 without dying. Don’t use your Poison Trail (Q) on minions until after you have some items. You should be trying to last hit by using your auto attack before buying your Catalyst on first trip back. Singed is very easy to harass and because of that, you'll need to have health potions. Try to get all the last hits on minions without taking damage.

Team Fighting: You'll want to focus your crowd control on the enemy dealing to most damge to your team. These champions will usually be AP and AD carries, but you also have to consider what champion in the game has the most kills and highest gold count. If they have superior items, you want to try and shut them down in team fights. When the team fight starts, you want to dive immediately onto that target. Start using your posion trail (Q), then use Mega Adhesive (E), then try to flip the champion out of the team fight with Fling (E). If they are far from their allies, then you want to flip them twoards your team to be quickly picked off. Your goal is to be on top of the enemy team – flipping, slowing and trying to be the target of damage. If you can distract that carry into hitting you instead of your allies – you are doing your job, even if you die in the process.

Saving your Fling (E) can be better than throwing them. Sometimes it will cause them to Flash prematurely and be out of escapes.
Watch out where you are flinging, sometimes it might save their lives.
Singed is naturally tanky at level six thus allowing you to build gold per 5 items and AP items.
You are a force to be reckoned with at most of the stages of the game. It just depends on how farmed you are.
When split-pushing always keep your sides warded in case of ganks. Split pushing allows you to pressure the enemy team.

Synergies: Orianna, Lulu, Amumu

Any champion with a speed boost or crowd control effect synergizes well with Singed. Using speed boosts and crowd control will maximize the amount of damage your team can deal to a target when used in succession with Fling (E).

Counters: TEEMO, Elise, Vladimir

Long range harass can counter singed early game. Vlad can poke down singed and sustain. Elise poke % health dmg is strong. Vayne can smack a singed around early level, and late game

Hope this guide helped you and have fun destorying and annoying people with Singed xP