Ogre Magi is a melee intelligence support hero. He is famed for being a luck-based hero capable of dealing huge burst damage… if the RNG gods smile upon him.
Being largely item independent and having decent stats, he makes for a viable support or utility hero.
Skills
Fireblast is usually skilled and maxed first.
Ignite is usually skilled and maxed second.
Bloodlust is usually skilled and maxed last.
Multi Cast is almost always skilled (levels 6, 11 and 16).
There are a handful of cases where you should skill differently. See here for more detailed information on this. If in doubt use the above skill build.
Items
Starting Items: Observer Wards and/or Courier, Tangos, Healing Salve, Iron Branches, Clarities.
Early Game: Flying Courier, Observer Wards, Boots of Speed, Orb of Venom, Magic Wand.
Core: Arcane Boots
Core Extensions: Force Staff, Mekanism, Drums (one of these should come first).
Luxury Items: Aghanim's Scepter, Medallion, Heaven's Halberd, Eul's Scepter, Vladmir's Offering, Scythe of Vyse, Ghost Scepter, Rod of Atos, Veil of Discord.
Situational Items: Gem, Sentry Wards, Dust (vision), Smoke of Deceit (ganking). Pipe of Insight (if didn't buy Mekanism), Boots of Travel (late game 6 slotted), Necronomicon (pushing).