I'd personally say start with a duskblade base, since most AC adjusting spells are low level. Increase HD, remove Armor Prof. Add in Abjurant Champion class features, remembering to make the class bonus to spell-based AC apply to non-abjurations (because who wants a class that gains extra AC from only Shield, since Mage Armor is conjuration). Add in some defensive class features like the Knight's Bulwark of Defence and Vigilant Defender, the Dragonlance War Mage's Arcane Aegis, perhaps a variant of the Shield Block and Shield Counter manoeuvres. Allow part of the Armor and/or shield bonus to apply to touch attacks.
For a spell list give AC-granting spells (Mage Armor, Shield, Dragonskin etc.), some restraining spells (grasping hand, telekinesis, hold person/monster, solid fog, etc.), some minor teleports (to interpose you between the monsters and the squishies), protection spells (resist elements et al), some weapon and stat buffing spells (GMW, Bull's Strength et al, keen edge) and some debuffs(enervation, ray of enfeeblement, dispel effects).
