I'm new to Morrowind and I'm planning my first character. I know there are a lot of threads like this one, but I didn't want to intervene into someone else's thread and ask for attention.

Is this a good character build for a thief like character who uses magic too? Or will she be weak?

Race: Dunmer
Birthsign: The Lady
Class: Custom
Major skills: Destruction, Sneak, Alteration, Short Blade, Marksman
Minor skils: Mercantile, Speech, Light Armor, Athletics, Restoration
Specialization: Stealth
Attributes: Agility, Willpower

That looks like it would work fine, at least to me. Just a couple notes:

- You might end up a little light on magicka because of a low intelligence and no magicka multiplier, but since you're indicating that the magic use is going to be secondary that probably won't end up being too much of a problem.
- Having Destruction as a major skill, when you already have a ranged and melee weapon skill, is a bit redundant. I'd recommend replacing either it or Marksman with Illusion, depending on your preference.

I agree with Maccabeus. That's a pretty powerful character, but you would get much more use out of illusion than with both destruction and marksman.

And you will run out of magicka fast with that build, so always have magicka potions equipped. I suggest getting rid of Athletics and replacing it with alchemy.

All athletics really does as a major or minor skill is make your character level-up ridiculously quickly. It doesn't really need the boost.