I want to be a dark Elf as a thief and be like a sneaky mage or something. A dark Elf thats evil. A half thief build and mage.

Your going for the Mystic Archer build:


Marksmen
Sneak
Illusion
Blade
Light Armor
Destruction
Mysticism

Something to that effect would do the job the top four skills being the core and the bottom 3 are optional fillers.

You might consider not making Sneak a major, since it levels so fast anyway. If you sneak your way through the tutorial, you'll probably get it to Apprentice without even trying. Two of the rats are "blind," and can be "herded" ahead of you to increase your sneak training.

A thief is going to need to train up some kind of lock-opening skill, either Security or Alteration. If I were roleplaying a theiving mage, I'd go the Alteration route. It doesn't need to be a major, but you'll practically have to spam an Alteration spell to raise it high enough to be much good. You can always fall back on lockpicks for locks that are above your current spell level.

This is what I would go with for a Dark Elf Thief type character
Birthsign Mage +5 Endurance +5 Luck
Majors
Blade
Destruction
Block
Sneak
Light Armor
Illusion
Restoration
I know your probably wondering why no security or alteration well those skills level up too fast and when you reach LV 10 Security becomes irrelevent.

So your looking for a Thief Mage. Here's my suggestion:

Sneak
Security
Light Armor
Destruction
Illusion
Mysticism
Athletics

I do this on a regular basis. here is my usual build.
Acrobatics
Alteration
Athletics
Mysticism
Illusion
Marksman
Sneak

Personally I see no use in taking skills that a Sneak/thief doesn't need to use.