Wow... My server just invented a script that is going to stop mages from using Auto still spell... That makes building a mage that can actually do anything on that server very difficult... Anyone of you guys know how to build a mage with high ac without Auto-still? I do want to be at least 20 caster... And preferably the epic warding spell... Man, it's gonna be hard... Depends on what the critters and mobs hit with. +20 or above will get through virtually anything; even warding. If that's the case, fire your scripters... just kidding; it's their world play by their rules I guess.
Go palemaster; with lots of dex, and little int/cha (depending on mage type). 20 levels should net you around +10 or thereabouts; coupled with epic mage armor you could hit almost 40ac buck naked (there is a build here that hits 70ac naked with just epic mage armor; imp expertise and palemaster bonus ac). Take two monk levels; and you will have the arrow catching feat too - catching one arrow per round..

Still, not sure why you want the ac; you should not be getting into melee as a mage... The reason I need ac is that the npc's on that server has seriously high ab, so the fighters cant get enough ac to resist them. And when the npc's has a very high damage too, the fighters get their @sses whopped. Thats why I need high ac. I need to be able to survive long enough to raise the fighters, and inflict some damage before I die... *refraining from comment*
You'll have to go pure mage, or deal with the lower ac another way - monk with high wisdom or something. Yes, your best bet is probably Monk/Wizard/PM. You'll want at least 2 Monk levels for Evasion and at least 10 PM for crit immunity. Thus, something like Monk 2/Wizard 28/PM 10 should work.

Make sure to pump some points into Dex and Wis for the AC increases. Dex is nice because it will increase your Reflex save, but you don't lose Wis AC if you're caught flat-footed, so that helps as well. Only 1 level of monk will get evasion - but 2 of rogue gets evasion. Hmm... I currently play as only evil characters, so it'll be a little harder, but..

Can I not go something like:
35 sorc/3 BG/ 2 monk

Bonuses: Devine shield (Extra ac)
Epic mage armour (Extra ac)
Epic Warding (Damage reduction)
Monk ac bonus (Extra ac)
Dex ac bonus (Extra ac
Devine grace (Charisma bonus to saves)
Improved expertice (Extra ac)

And if I focus all my abilities on charisma, all my skills on tumble, discipline, concentration and spellcraft, feats on spell penetration and spell focus, I will have quite a battlemage without using armour at all.

Right? Yep; just remember the Monk ac bonus is based on Wis.. so you will need to pump your wis a little bit (owl wisdom spell helps, but they only add +2 to +3 at most; unless empowered).