singed is a character who is a strange type of tank. early game you use your poison trail and fling for quick farm. you want to go a catalyst early game because of its mana regen per level feature along with its health regen. as singed you are not meant to basic attack unless you hitting a hostile building unafected by your poison(turrets, inhibitor, nexus). late game you want to be tanky in a specific way according to how the enemy team is built. for example if the enemy team is built almosst completely AP then you are going to want to go with the magic resist build so that you can easily initiate in battles while ignoring their damage. same thing goes if they built almost complete attack damage. your going to want to use the armor build. if they have a well balanced team(like in ranked) your going to want to use the hybrid build.
NOTE: SINGED DOES NOT DEAL DAMAGE USING HIS BASIC ATTACKS HIS DAMAGE COMES FROM POISON TRAIL AND FLING.

pro:
good early game farm.
a great solo top.
very good mobility.
can escape five man ganks with ease
con:
very reliant on his team for how good he does.
your ego may get the better of you(you might try to solo the entire enemy team).

in team fights you are one of the most useful initiators. you can use your fling to fling the ad carry or another useful member of their team back to your team to kill. this picks of one of the people they would rely on in a team fight and makes them reconsider attacking your team. if your using the armor build or hybrid you can tank turrets, baron, or dragon for a short period of time in which your team could then backdoor, and secure baron/dragon(this is not recommended for Magic resist signed). your slow also allows your team to catch up to the enemy team. you can run directly into combat with your poison trail to confuse and weaken the enemy team while your team charges in behind you to secure the kills.

i go with magic pen runes so my poison can do maximum damage early game.
i get seals of armor so i can at least have a little early game support because you can easily be focused down before you get your items.
get magic resist per level so once you get to level 18 you have a decent amount of MR.
the quints of swiftness are probably some of the best runes you could ever own because they allow early game escapes and allow you to start without boots or start with boots and have movement speed that allows for easy escapes and as singed your goal is to get in front of them with your poison trail and having faster movement speed makes catching up a cinch.