This is a skeleton build -- as in, a build with some bare essentials and then a little more to give you more of an idea of what to shoot for.
Feel free to modify it in any way to your liking, of course.
Class 1 Rush
Class 5 Destruction Magic
Class 2 Magic Control
I recommend putting Rush at Class 1 and not raising it any further because it's an utterly useless expertise for DDers. Any Rush skills obtained are CLS-R-based, whereas DD is heavily Spell-based with only a smidgen of CLS-R-base. If you do happen to have a build that incorporates both STR and MAG, not only do I recommend you recheck your game knowledge, but DD is much stronger anyway. You have no need of any Rush skills by this point. Unless of course, you're an all STR build. Which leads me to ask... why do you even have DD?
I put Destruction Magic at Class 5 because that grants you your first Almighty-affinity skill, Megido. Of course, if you hope to fully flesh this build out, I'd recommend at least going to 8.5, 10.0 if you're hardcore and don't mind dropping a whole 1.5k Expertise on a single skill.
I put Magic Control at Class 2 because it grants you your first MP reduction skill, VERY handy to have. I strongly recommend kicking it up to at least Class 5 if you can manage it for further MP reduction.
If you have room, I strongly advise adding COTW Class 3 at least, or Enhance 2.5 to this build later on down the road, since you'll have the extra Expertise to do so. I actually have a build I'll be posting sometime soonish that includes a mixture of all of this.