This is my build for Singed I've always looked for a build on here but could never find on that I like. So here it goes. =)

As you can see I use typical runes to give me more ability power, magic penetration, and the all important mana regeneration.

My mastery page is very simple. I choose to focus on my AP because defense comes from the items in the build. which i why i do a traditional 21 in utility and 9 in offense

Now for the all important items. I start with a sapphire crystal for mana and health potions for well health regeneration. Then i buy my Catalyst The Protector and then build by Mercury Treads. Then I make the Catalyst into a Rod Of Ages and start working on my "tankyness." This is started by buying Thornmail and then Force Of Nature. This is a simple Tank build but it works great with Singed. Then i buy Lich Bane for more movement speed and mana which also turns into health because we all know Singed has his passive which turns 10 mana in 2.5 heath. Then I finish with some final Ability Power and get a Rabadon Deathcap which finishes the build. And congrats you should be owning everyone and Dominating in team fights thanks to your Ulti.

My skill sequence is simple. Start with poison cause u level faster from 1 to 2. After the level get fling so then u can have some fun. then at level 3 get your important slowing ability. Then get poison to level 3 so then at level 6 you get your ulti. Then alternate from fling to poison till both are maxed. Afterward level ulti again and finish fling and your slowing sludge.

As Singed you definitely need the speed from ghost and the extra damage from ignite. I for one HATE ignite I think it's a lame spell but everyone uses it and with Singed the extra 200+ Damage just helps you and your poison.

Pros:
Great team player
Massive Damage maker
Makes everyone scramble if played correctly
Cons:
Gets focused a lot
Loses mana fast at early levels
(HONESTLY) Singed sucks until he gets his ulti

You are the front line man. Use your ulti in the beginning of a team fight and just run around like a madman. Not only does it hurt the other team. They begin to panic while your running around trying to click on you anddddd the rest of your team should be attacking by now.

And that wraps it all up! Hope this helped you in your ownage as Singed. Remember, be a team player, be careful at early levels, and most importantly, be smart.