This build is based on being tanky enough to survive, but having the punch to kill enemies by yourself. Singed is the best kiter in the game dealing damage more easily on the run then anything else, but he can also be a very good chaser if used correctly. when fighting as singed auto atk is NOT your main source of damage. The main source of damage is your poison which you must try to keep on all enemies at all times in a team fight, they may not notice but it does a significant amount of damage. Flinging squishies towards your team and laying down some goo to keep them there so your team can devour them is something you must always be trying to do. though singed isn't the best initiator it can be done if no1 else on your team is equipped for the job.

Pros
-Very hard to kill mid to late game
-Good CC and ability to fling enemies back to the wolves.
-Good sustained damage
-Very fast when ult is active.
-Very good pusher in mid to late game, Can push an entire lane back to the tower just by running past creeps.
1 to 1 AP ratio on fling

Cons-
No ranged atks, discounting mega adhesive.
Higher elo players make it difficult to fling them.
Fling has a very short range.
Isn't very effective without support from damage champions.

The runes a select for this build are based on surviving and doing as much damage as possible in the process. I go magic pent reds, dodge yellows, and CD blues. Bringing flat health quints.

Getting anything else for reds is a waste, I go for dodge because they add the most to survivability, and having lower CD's is always a good idea. The flat health quints really help your early game survivability because singed has fairly low health at low levels.

I get AP, CD, and magic pent mat. in the offensive tree because they help to kill faster, plain and simple. I go for resistance over armor in the defensive tree because singed rarely has problems with auto atking champions magic resist is more important to survival and i get strength of spirit for its synergy with singed's passive and ardor to kill champions and towers just that much faster.

My item build on singed goes like this, Get a regrowth pendant right off the bat, then go to lane and try to get first blood if you can, but that depends largely on your lane mate as singed doesn't have great early game power. When you get over 700 gold go back to base and get boots and a philosophers stone, this is a great item in that it makes you able to go in to poison minions or make grab attempts without fear of being harassed down due to your ability to heal so quickly, it also gives much needed man regen so you wont be out of mana at a crucial time in a team fight, either trying to save a team mate or seal an enemies fate. The gold per 10 is also great this is a very good item which gives a lot for the price and eventually will pay for itself. Next on your list is merc treads which is always a good item due to the inherit magic resist and the CC reduction (singed is always CC'd in team fights). now after this is situational if the other team is very AP heavy go for banshees veil, if its very physical heavy go sunfire, or thornmail. If the team is fairly balanced or you are confident they wont be able to kill you, get a Rod of Ages, or Rylais crystal scepter, rod of ages gives better stats but the slow off the rylais is great for crippling fleeing enemies and getting away if you find yourself in deep ****. Now as to the concern that ppl wont chase a singed with rylais because of the slow, with my style of play i only truely run away when im VERY close to death, and that slow makes all the difference.

The first skill to get in fling, then poison then mega adhesive, once there is one point in each skill, max out your poison cloud. Getting insanity potion whenever available. when thats done put one more point in mega adhesive then take fling all the way, then put your remaining points in mega adhesive.

This is where i deviate from the vast majority of singed players, I bring Ignite and Ghost. Bringing ghost on singed is a no brainer no real explanation needed there. But, the reason i bring ignite is to finish off a champion who is very low but i cant catch, or my personal favorite, turning the tides of a one on one fight in a nasty way, an enemy champ is chasing you down when you have very little health and they have a good 5 bars, they charge in with zeal knowing singed doesn't have the power to nuke them down, but as i have brought ignite i do have exactly that, lay down a poison trail which they will ignore because you are so low then simply ignite fling and run the opposite direction throwing down mega adhesive if needed and laughing madly at their frustration as they die a so painful fiery death.

To summarize, I build an AP oriented singed with survivability in mind only building seriously tanky items if I deem its necessary but the game plan is to poisonate the country side either in 1v1 fights or in teamfights keeping everyone poisoned at all times is priority number 2 number 1 being keeping your teams squishies alive (you are still a tank). The key is to know what you can get away with and what you should do anyway even if you know it will result in your death, if it paves the way for your team to stomp face.