This guide isn't for everyone. That being said... if you want to try something new and you're a team player, not a KD ratio *****, keep reading.
Spells, Teleport or Heal and Clarity. Saves you from a gank early game or a fast travel for item guys, and the mana regen boost is something you MUST get early game.
Siphoning strike. We are going to completely forget about this button. Do NOT get this skill until you have no other choice.
Your first skill is your AOE. Your second is your slow. Always choose to upgrade 1) Your ulti, 2) your Aoe then 3) Your slow.
Start the game off with a regrowth pendant, and harass early with your AOE.
The items are pretty simple, but you need to return somewhat often. I'll list them all in the order to get.
1) Regrowth Pendant - Turn into Philosopher Stone
2) Boots of Speed or Mercury Treads(depending on opposing teams champions)
3) Rylai's - You're AOE with also slow them, and the HP keeps you alive.
4/5) Warmongers - If you are dying early... get a Warmongers 4th.
4/5) Rod of Ages - If you are staying alive, go RoA first.
6) The last item is pretty flexible. Either go Banshee's, More AP, or Cooldown Reduction, based on the need, which I'll explain below.
You want to lane by yourself with this build. You can easily one shot waves of creeps after a few levels and items, and your AOE harasses enemy champs pretty good. Buy items often with this build. Each +AP helps.
Now... once you get level 6 you should go straight for a golem buff. The cool down reduction and +% of mana is priceless. You should always attempt to have a golem buff on. You can constantly harass and push.
As a tanker/Mage... You won't be getting many kills 1v1 unless your ulti is up and the players are stupid. Your job is to push lanes and stop pushes. You can literally deter an entire team if you defend on top of a tower. In team fights just spam slow on the target, and drop your AOE to gain control of the area you are fighting in and cause pretty heavy damage. It's a great offensive and defensive spell.
I'll update the guide again once I'm home and have more time. Figured I'd put something up at work. Hope someone finds it useful.