Not Updated For Current Season
This build is focused almost entirely on kiting and survivability. The basic idea is to play singed as the one to pick the fights, and single out enemy champs. Late game he is relatively low damage, but with high stacks, let alone 20 stacks on leviathon he is almost unkillable if played well. With Warmogs charged up, your usually sitting on 5k hp late game with nearly 200hp per 5 regen. It takes a full team to take you down, or someone with Mandreds and a high attack speed. So take care around experienced Warwicks.
Scene one - Laning
Ok, with this build Singed's ideal laning partner is a high dps. Your gonna pick the fights, single out enemy champs, and turn the 2 on 2 into 2 on 1. Don't be too aggresive though, your still pretty low HP early game.
I take fling for those hijinks in the bushes. He is one of the few champs that can charge bushes even if you've arrived late. Or should I say I've never failed to escape yet. If it goes bad, hit ghost and run for it past your full HP lane partner. If they chase, fling should finish it's CD and if you have over 1/4 HP you can usually throw them into the turret. So many times I've been able to kill both enemy in my lane when solo'n cause they pushed in too far and get thrown at the turret. Especially when your solo you've out levelled your enemy and hit 6 first so you can chase down the other half the time.
But all that aside your main priority is not on kills, but on farming. At the start of each minion wave your should be just infront of them, hit gas and run back towards your turret. By the time the minions catch up they are half to quarter hp and easy to finish off safely. Whatever damage you take laying down the gas you regen pretty fast. If your badly hurt then stay back and let turret do the work. But as I say your main priority is farming, because this build is pretty expensive. Also, try to get up to 1200 GP before you go back so you can buy Merc treads straight off, then tele straight back with full HP.
By the end of early game you should have the regrowth, Mercs treads and Leviathon without too much hassle.
Pro tip #1 - When laning with a teemo, after he's put a mushroom in the foward (closest to the enemy) bush, stand ontop of said mushroom. When enemy comes by or towards the bush hit gas and charge out, and then fling them. Cause you started on the mushroom and your running straight at them they will end up being flung onto the mushroom. And gas poisoned. If need be hit your ult and finish them off.
Scene two - Mid game
Ok by now the laning will have broken down a little and people will be roaming the map trying to gank. Generally by now you should have taken down the outer turret also. While your starting to get strong enough to turn team fights you should still be spending a lot of time farming. Look for any big creep buildup and go take them out. The best part of gas is you can take down mobs of 20-30 creeps in about 10 seconds by running a few rings around the outside of them.
So basically your time is spent half in team fights, half in farming minions. You still have a lot to complete in your build but your strong also. You should be getting stacks in leviathon and be around the 10 mark.
Pro move #2 - Tryndamere
Mid to late game you can get easy kills on Tryndamere with a little skill. Kiting, the act of tagging an enemy and making them chase you, is very effective on him in particular. If you can get him to use his ult then all you need to do is survive and let him get posioned. Poison is a DOT and it will usually hit him after his ult wears off before he can heal himself, giving you an easy kill. Keep in mind your game has to be going well in general and you have a lot of HP and regen first so you can survive his strong attacks. But if he chases which he nearly always does, that works in your favour.
Late game he will be aware of this, so don't run so far, turn and fling him when he ult's to keep him close at hand, cause he will use that ult to flee. With a good team with cc, they will stall him long enough for the ult to wear off and finish him.
Scene three - Late game
Ok if you have your basic build done, and by that I mean boots leviathon warmogs and force of nature you are now a scary beast on the battlefield. You should be high if not 20 stacks on leviathon. Once you get 20 stacsk btw, that's 20% damage negated. Pretty nice eh. I've literally run rings round a Gangplank and a Shen and there was nothing they could do. I've made countless escapes from 5v1 fights by hitting my ult and ghost. That makes him scary fast and is also very good offensively when you can't break the enemies line.
Late game items
Once I finish Force of nature I look at what the enemy is doing. This is customise time. If you are getting a lot of magic damage then up your magic resistence or get even more HP. If you're facing some high dps types then get thronmail and watch them kill themselves trying to take you down. If they have excessive cc then get quicksilver sash. If they are a good diverse group then ramans omen os a good all rounder for slowing anyone trying to catch you. For every champ there is a counter. For every team there is a counter. Look at what they are usuing and work against it. Your team is counting on you to do this. Since you are the front line you need to be able to take the opening salvo of most teamfights.
But, odds are you won't get this far. Most games I play singed the other team surrenders before I can complete my build. Often I don't even get to complete Force of nature. Once they see there is a enemy they can't touch protecting some dps that cuts them up, 7/10 times they will give up.
Pro tip #3
Re-read what I just said. With 4 items your very stong. So the last 2 items are always tailor made to meet your enemy.
Don't be shy in using your teleport. It has a long CD, but it's better used than unused. With practice you will start to see key moments that good use of teleport will change games. This is keeping useful turrets alive. Late game outer turrets are too hard to defend so don't go to save them unless your sure of survival of both the turret and yourself. Mid/late game your turrets help keep the minons at the enemy's end of the map making for easier pushes on isolated turrets when the enemy team is otherwise distracted and busy.
Singed is crazy fast when he pops both ult and ghost, plus he runs through creep, and will almost always get his fling off.
Fling is Singed's key skill. You can use it offensively and defensively. Throw weak champs towards your team for a quick kill. Keep strong enemies away from your teams DPS by catching them and fling'n them back. Don't noob yourself and fling an enemy at an already near dead ally.
You are strong but not invincible. Pick fights but try to avoid 5 on 1 situations. Also take care around anyone with mandreds and anyone with slows like Ashe or frozen mallet.
This is work in progress and if I rememebr anything else I will post it here.
Thanks for reading and have fun. Singed is one of the most fun champs to play imo and especially late game.
Lastly about the masteries..
I don't take greed cause I don't need an extra 180 gold in 30 mins. I get that in 2 minion waves.
I do take 1 point in mana regen cause it helps early on. .33 per sec is 1.65 mana per 5. It helps.
Runes wise, someone else said and I agree, flat mana is great early on, plus his passive gives him more HP for it. I used to run manamune/ archangles build just to up his mana and by that his hp, but don't really think they helped as much as I had hoped. Still they work well and I've won games using them both, but I have gone off them mostly due to their price.
I started my build off a build from Modafire. I've no idea who's that was, but I changed it slightly to fit my play style. There is a good chance someone else has alrady posted something very similar to this and if so they deserve that credit and not me. I'm posting this cause its a champ I love to play and I'm suprised that I don't see more singed out there. I know I've converted a lot of people just by them seeing me in game and what I can do, especially late game.