First off, I know this isn't a typical build, but it's an awesome one! The first few items are meant for an easy first blood. Ghost, Fling, Ignite + allow the champ your laning with to do as much dmg as possible. The reason I chose Philosophers Stone as the first real item is simple: The health and mana regen allow singed to stay in lane and troll. I played 4 games in a row with a Teemo in my lane and we DOMINATED... pure obliteration!!

Since you will be getting more assists than kills, the extra gold from Phil. Stone really helps in the end.

Heart of Gold is the next choice, mainly because of the gold increase. By the time you get Omen, Heart of Gold would have payed for itself and then some.. Same logic applied to Philosophers Stone and Reverie. The only difference is Philosophers Stone is VERY useful

CD runes are real good for a few reason:

1) Since you're going support, you want your ult and adhesive to refresh as soon as possible. Nothing more terrifying than seeing a Singed come at you with 500+ MS, flinging you into a Teemo, and then keeping you there with Adhesive. If you do manage to escape, Fling would have refreshed already.

2) You simply don't need AP with this build. The extra DMG obviously would help, but your main focus is support.

I already explained the first few items. but the reason I went with Philosophers Stone before Catalyst, is because it essentially does the same thing - It allows Singed to stay in the lane and troll and is WAY cheaper. Phil. Stone and Heart of Gold allow you to get the rest of the items with easy, and make Reverie and Omen not as painful to purchase later in the game. Phil. Stone and HoG usually pay for themselves and then some by the end of game.

By the time you have your Rod of Ages and Banshees Veil, you'll be able to tower dive with ease.

Singed will become an incredible initiator using this build.

Ghost for obvious reasons.

Ignite can be swapped out for anything really, but I recommend it for a very easy first blood to get the ball rolling.

Singed's MS and making Ignite and Ghost as powerful as possible was the focus here (the only point put into Offense are for Ignite and Ghost). Everything else is a great bonus.