When built just right mid game Singed will get your team more ganks and late game Singed will push through enemy minion waves insanely fast.

To make sure a gank works use fling to isolate the target in between you, your teammates and the minion waves, making escape for them more difficult. If the target starts to get away use your summoner spells and mega adhesive to slow them, speed up and fling'em back in.

You can also save your teammates from ganks. Use fling to get enemies off your teammate and mega adhesive to slow them, then use insanity potion and poison trail to get yourself out and keep them off your back. If close enough to turret or if one of them walks through the poison long enough double back and fling them so you're between them and their base. Then make them pay for trying to gank your team.

Farming's very simple, toggle on poison trail and right-click the furthest minion. Walk back and forth as poison starts to ware off. This will help get the gold you need for this rather expensive build.

If fighting champs with immobilizers or a lot of magic burst damage substitute boots of swiftness with mercury treads.

The health, health regen, mana and ability power stats shown aren't 100% accurate. With Empowered Bulwark Singed's health will be much higher also with Archangel staff and Strength of Spirit all four will increase as you use spells.

At game start don't pick a skill, wait till you reach gank bush. If and when you see an approaching enemy champ pick fling, if none show before the minions pick poison trail and start farming.

Pros
Farm faster
Do more damage w/spells
Make ganks easier
faster than a full tank Singed
Cons
not as tough as a full tank Singed
can't damage buildings much
to be more affective against buildings you can sub Archangels and Lichbane for Manamune and Trinity force

This build was designed to maximizes Singed's team contribution, burn through minion waves and keep him in lane longer by taking full advantage of his large mana pool and his own passive.