This is an AP singed build with a little side tanking.
first build means my guide will suck, but either way i love this build

Skill Order: I belive it is best to grab throw at level one and the max gas as soon as possible while grabbing you're slow every other chance, throw comes last no matter what

Early game: this potion and mana crystal are a Must have, while i belive the spell order is singed's most effective as well. Always take a side lane and pick a lane buddy who can deal damage or has a stun. singed cant do much at all early on without some support. keep at you're lane till you're level 6, now if you have a damager ally then its always a good chance to pop you're ultimate and initiate a 2v2 as long as you're not near the enemy turret.

Middle game: My opinion is split at mid game because although singed is a great ganker he becomes severly under leveled really fast if he ends up not killing anyone.

Late game: Now you should have decent AP and be able to beat nearly anyone but a DPS champ in a 1v1. you're speed makes the greatest weapon with a huge amount after popping ghost and leaves you unmatched at chaseing, tower diving, and initiating.

Items: alright guys heres the breakdown
Start: Mana crystal, 2x Hp potion
boots of swiftness
Rod of ages
Midgame:
you'll either need Void staff or Abyssal scepter.
Magic Pen is a must have
Rylai's scepter
Lategame:
The new Zhonyas Hourglass or Thornmail (counter DPS)

Depending on the way the game turns out. you're own tweaks will make you a AP Tank Hybrid no matter the turn out. most games ive played with this i've gone out with a positive KDR and a pretty large amount of a assists. if you focus on singeds tank aspect you will have very few kills and you will be gold starved for most the game, however the mass amount of assists is amazing

Great laning partners: Nidalee, Blitzcrank, ezreal, Corki, Ashe, Xin, fiddlesticks
NEVER EVER LANE WITH: Sona, Soraka, Zilean, Taric (insert continued list of champs who are supports that deal no damage)

First game after posting this build