"Ask yourself 'If I was playing anybody else, would this be a good idea?'

If you answered no: then do it.
If you answered yes: then stop doing it."

*This guide is a work in progress*

I've read a few of the Singed guides out there. Some were good, many were off the mark. This is a compilation of what I have learned by personally playing Singed in ranked games, modifying my build to find what works best.

From my personal experience, this build works well at my level of ranked play (ELO 1000 - 1250). I believe I have adequate experience with Singed, and have much to offer about him. However, I will of course check back on comments and update my guide depending on what I learn from the community, and further play.

Singed is a tank, and can soak in tons of damage without worry due to his incredible escape potential. First lets take a look at his abilities...

Passive - Empowered Bulwark

For every 10 mana that Singed has, he gets 2.5 health. This counts for base mana, as well as bonus mana; therefore, Singed actually has the lowest base health in the game. Any mana items you buy on Singed are more cost effective than on any other champion (other than Ryze). Buying purely mana items however, would be utterly stupid. A few will suffice so you can eventually leave your poison trail on all game, but too much is just a waste of gold. You will be much better off buying more defensive items.

Q - Poison Trail

This is how Singed farms. Early game, this will drain your mana too fast to keep it on for long. Turn this skill on as you approach minion waves, poison the lot of them, then turn it off and stand back. The poison will do they work for you, and you get to reap the benefits.

W - Mega Adhesive

An insanely powerful slow pool. Use it to help your jungler gank your lane, and to escape from your opponents' jungle ganks. Mid and Late game you can use this in teamfights to stop the enemies from positioning themselves well, and also during chases/escapes to ensure kills or escapes.

E - Fling

Singed flings an enemy over his head. This skill does a small amount of damage, but the utility of this skill is what you really want. The main use of this skill is to punish out of position enemies. Fling them into your teammates, into tower range, away from teammates who need your help, etc. DO NOT fling the enemy tank into your team during a teamfight setup, especially near your ranged squishies. In fact, don't fling ANYONE near your ranged squishies. Fling is used to better your team's overall position, so try not to kill your own teammates with it. NOTE: Fling has great synergy with Mega Adhesive, as you can either slow an enemy to ensure a good fling, or after flinging an enemy into turret/ally range and Mega Adhesive to keep them in place.

R - Insanity Potion

This is why Singed always runs, and never dies. It raises nearly all of your stats, most notably your movespeed, health regen, mana regen, and tenacity. Furthermore, this skill lasts 20 seconds once you activate it. Therefore, you can use this to initiate a teamfight, and still have it active when it comes time to chase/escape. Early game you can use this to sustain in lane (it provides nearly twice the mama it costs, and makes you nearly unkillable when you use it effectively). You can also turret dive when active, but in most cases you would be throwing your life away without the help of your jungler.

Early game, you have to be careful to not push your lane or you WILL get ganked. This is why its best to take solo-top lane with Singed and have a teammate jungle. Doing this you can activate poison trail to farm waves when pushed back, gain decent amounts of gold, gain a level advantage over your opponents, and still not overextend. It is easiest to stay alive early game with Singed by turret hugging before reaching level 6, so try to let your enemies push you back before poisoning the minion waves.

Once you hit level 6, you will have your main source of sustain, turret diving capabilities, and can start to play more offensively with the help of your teammates.

Work on getting Catalyst and boots as soon as possible, and upgrade each of those to Rod of Ages and Merc Treads. These are Singed's two staple items; I wouldn't be surprised if you actually get reported by your teammates for not getting a Rod of Ages.

You start to get much tankier when Rod of Ages starts to stack up, and you start buying more tanky items. I choose to build Rylai's Crystal Scepter next on Singed because all of the items perks greatly help Singed. First off, it gives 500 health, health Singed needs. 80 ability power, great, more powerful poison and fling. Finally, the best for last: your poison trail now slows every enemy that walks through it. By buying Rylai's, you've increased your teamfight potential and utility, and doubled the power of your escape potential.

From here, join with your team and protect them. Punish any enemies out of position. If no one on your team has been warding, grab a few and set them up in prime warding locations. There are plenty of warding guides out there, so I'm not going into detail here.

Once Singed achieves full build, if he sticks with his team he cannot die. Continue to punish enemies mistakes. Initiate fights with your ult if your team has no initiators. If you can get enemies to chase you, laugh as they die slowly to your poison trail.

Do not run straight into unwinnable fights with Singed. You can survive these fights by running away and using your abilities, but you will rarely come out on top. It's not worth throwing away valuable health or even your ult just because you facechecked a bush with three enemies in it.

As for what items to fill your last three item slots, look below...

Rod of Ages and Merc Treads are nearly necessary. Do not play Singed without buying these.

Ninja Tabi can replace Merc Treads in rare cases, but since dodge is being removed from the game anyways, stick with the Merc's for now.

Rylai's is always an extremely powerful item on Singed, but not as necessary as the other two listed above.

Singed is a tank, and therefore needs armor and magic resistance in addition to his health. Here are a few choice to choose from:

Armor -

Frozen Heart - 99 armor, mana = health, CDR for ult, amazing passive, (best choice)

Thorn Mail - 100 armor, amazing passive against 'right-click-2-win' (situational)

Randuin's Omen - 75 armor, more health than FH, but no mana, good passive and active (situational)

Magic Resist -

Banshee's Veil - 50 MR, health, mana, more health due to mana, amazing passive (situational, though I pick it most often)

Force of Nature - 76 MR, health regen, move speed (awesome), Passive super health regen (reccomended by most, but I take Banshee's veil for it's passive)

Quicksilver Sash - 57 MR, if Banshee's Veil passive isn't enough, add this to escape anything.

Item's to avoid -

Gaurdian Angel - It gives both armor and MR, which is nice, but the passive is near useless with Singed. If you actually die and it revives you, your chances of getting away are less than slim.

Sunfire Cape - Not a great item at all. That passive needs to be changed before this item will really be useful on anyone again.

Abbysal Scepter - Mr and more AP seems really nice, but it doesn't give too much in the way of defensive power, and Singed should not be played AP carry.

A few other notable choices -

Will of the Ancients - Plenty of AP, and Spell Vamp is laughable on Singed. Poison trails can easy heal you back to full health. The best part is the aura that spreads these stats to allies. Getting this item will make you slightly less tanky though, but still enough to survive fights and spellvamp your way back to full health.

Chalice of Harmony - If you can't bear to turn your poison off, you shouldn't be playing Singed. But Chalice of Harmony will help if you choose to anyways.

*I'll look in comments for other suggestions to add*

I'm new to writing guides here, so If anyone wants to offer any help please let me know in the comments.