This is not by any means a cheat sheet or a set in stone guide for singed. This build aims to gather ideas from fellow Singed players and doesn't cover gameplay since gameplay for singed varies from lane to lane - or even jungle. In short he is a champion with some hard cc who can disrupt other team immensely and provide some support like features and he can tank while doing that.

Pros: -His passive allows him to become quite tanky even if he goes straight support/ap route
-His aoe control is incredible.
-Hardest slow in the game
-Fling can throw a carry in the middle of your team, throw that pesky Fiddle ulti out of reach or save your carry from a certain death.
-He can kill while he is being chased.
-Ulti gives incredible sustain

Cons: -It's downright stupid to chase him, so you need either play low elo or give the opposition some incentive to chase him. If you are impossible to be killed, they won't chase you. If they have more than 30 neurons, they won't chase you either. So you have to play their greed.
-No burst. No natural auras. No hard CC.
-Movement speed is essential, since Auto Attack or AP burst is nearly insignificant on even games.
-Ulti doesn't break a game like Amu or Galio ulti's.
-You need lots of regen because in each harass you also commit to being hit.
-Long Cooldowns
-Ashe or any ranged carry with frozen mallet can eat you alive.

Ghost is a lock here, i can't see anyone arguing against it. It synergizes with Singed, just like ignite synergizes with Morde's ulti.

I picked Exhaust as a second spell because:
1) It can net you a kill, fling someone exhaust him - if he is still not dead, slow him and then toss him again.

2) In team fights it can seriously cripple opposition dps by crippling the ad carry.

3) It can save your life to exhaust an Ashe who is chasing you.

There are several viable choices here. Clairvoyance is never a bad pick, especially if you have a GP or Cait in your team. Cleanse or Flash can also save your life in stick situations, Flash can also surprise opposition carry. So it's quite a valuable choice as well. I can see some people getting clarity, but i'd rather take a chalice or philo-stone instead of spending a summoner spell there.

Well this is also negotiable. Personally i love MP, since i can't get it from boots or void staff i try to maximize my MP efficiency through masteries. 9/21/0 9/9/12 9/0/21 there is a whole world of possibilities. But most important stats to maximize are : Magic penetration, Movement speed, Survivability skills ( HP/Armor/MR ) , CDR.

Armor/MR/Damage Reduction/MS and tenacity from defensive tree is incredible and magic penetration from offensive is too good for me to pass.

Well there are several possibilities here as well. Not in Marks tough, it's MPen written all over it.

You can go hp regen/hp/armor or Mana regen on seals. Depends completely on your play style.

As for Glyphs, for some extra kick AP or less painful cooldown CDR or more survivability MR.

For quintessences there are several ways to go. You can go armor/mr or flat hp for early game survivability. You can go magic pen for some more pain for the opposition or you can go movement speed - you can't go wrong with more ms on singed. I wish zeal had some stats singed could use on it. But only ms item Singed can use is FoN. The rest is **** for him.

This will be the bulk of our discussion. In LoL there is no single way to the victory. Those who built situationally have always the upper hand. For instance if you play a blind pick pug and on loading screen you saw a pesky mundo and vlad on the opposition team. Unfortunately you have no ignite, neither do your teammates. What would you do?

You buy exe.blade. instead of wriggles as off tank, end of the problem. Or imagine a scenario where the enemy team is filled with pesky CC'ers: Amumu, Sion, Sona, Vayne, Irelia. Can you even imagine skipping merc?

Therefore instead of writing you a recipe for victory, since there isn't any, i will explore usefulness of some items on Singed.

Only non-negotiable item on singed is RoA if you ask me. Within 10 mins the item gives 80 AP 630HP 725 Mana to a regular AP Carry or support. With Singed's passive HP bonus rises to 811.25. Which is only rivalled to Warmog's in HP department. Also deep Mana Pool means independency to the blue so you can save it for your mana hungry mid or AD Carry. Also Catalyst's early game sustain bonus is quite valuable to win your lane.

Gold per 10 items are nice if you playing bot alongside a carry. Of course you can farm well, but you carry needs it more, and you can still be efficient while being not incredibly well farmed. Your slow and fling are always valuable.

As for boots, they are completely situational as well. If you are fed early game - got first blood and farmed like there is no tomorrow you can grab sorc shoes and enjoy the extra penetration, so that your poison trail will do almost true damage. But if your enemy is heavy on CC you should go merc, if you are playing jungle or roaming, mobility or swiftness is the answer.

After boots and Roa, there are several scenarios to consider. If your AP carry has farmed well and you are winning, Abyssal Scepter can widen the gap further. MR on it and the aura is really powerful. Will of Ancients is also an option there, Singed and any character with an ap ratio in your team can benefit from it. But Abyssal Scepter should be priotorized since Singed also needs MR from it. His effective HP benefits a lot from it.

If their AD carry is slightly fed or winning his lane, frozen heart is a good counter. For singed it's not only a good item, it's a great one. The aura on is basically minus a dagger on each player on opposition team. Armor bonus is more than enough for mid game. CDR is beneficial. On top of that it gives the modest amount of 125 hp. Those HP's really add up.

Another viable item for singed is FoN. Movement speed and regen is invaluable, yet i believe it's more efficient to cap your build with fon, instead of going straight for it. Banshee's Veil is also a pretty powerful item in general and can be taken as a precaution to a fed AP Carry. I don't really recommend Thornmail since you should be mobile and toss people around during teamfights, and if you do your job well they won't be focusing you and you are free auras and substantial damage source for your team.

On a regular Tank, one would think, i need to be focussed in order to help my team. On singed, even if he is not focussed the damage he delivers during teamfights is really substantial, all you have to do and actually can do is to protect your carries from their bruisers. No melees allowed.

There are builds which promote Crystal Scepter but i really don't see any logic behind it, HP bonus is neat, but you pay for the slow which is included in the recipe. And you already have a built in are slow - and you only other active skill has a cooldown of half an hour.
Besides once you fling someone, he is supposed to be dead, not slowed. Don't fling bruisers into your carries (:

As for Deathcap, it may be viable, but it's overexpensive and with ap ratios of singed, team would better served to have several support items. For instance WoA + Aegis will make you more tanky, increase your teams sustain and tankiness and damage. I believe aura items are more valuable to Singed due to the nature of his gameplay. He has no burst, so AP stacking is far from efficient. He just needs to be there to deal damage. So maximizing his tankiness should be the answer to that problem. Yet building straight tank is also a waste of the potential. Since there are honestly better tanks out there. Singed can't beat Rammus in respect to survivability or cc. Yet Singed is more valuable choice in skirmishes and another factor is due to his passive, he can really be tanky even if he doesn't buy any hp items.

So an Abyssal Scepter on Singed is FAR more valuable then a Deathcap or Crystal Scepter. ( In case you are not fed )

I'm waiting for your comments, if you don't like ideas presented, feel free to downvote, but i'd rather see some constructive criticism. This game should be about counter building and builds which keep team comps in mind. You may as well get even a starks if your ad carry needs it. Duel calculations are fun yet in teamfights there are many other dynamics in play. Support/Tank role is a very good fit for Singed.