So I'm going to start buying some runes but I play multiple champions, I usually only play mages. Which means I need a good all around rune build for mage champions. I play champions like Brand, Morgana, Fiddlesticks, and Veigar, those are my main ones. I would just buy runes for each champion but I can't afford that.

Could anyone help out?

i used to main mages only, i used:
-mark: magic pen
-seal: mp/s per lvl (flat mp/s will work also)
-Glyph: CDR per lvl
-Q: magic pen or flat ap, i have flat ap cuz my 1st champion was janna and it helps out with her shield at earily game, but you would want to get magic pen considering you mainly play offensive mages

Reds: Magic pen
Yellows: Mana regen/level
Blues: AP/level or CD/level
Quints: Magic pen or Flat AP

yellows could be substituted for flat armor/mres too if you want some survivability

Flat AP

I play Mages the most and have tried most of the reasonable setups.

What can work in general

Marks: magic pen
Seals: flat mp5 or scaling mp5 (or some combination), flat armor, scaling health, scaling ability power
Glyphs: scaling ap or flat ap, magic pen, scaling mp5, flat cdr, flat magic resist
Quints: flat ap, flat health, magic pen

Explanation: For reds you always want Magic Pen, pretty much no alternative here, nothing else provides as much damage increase for the slot. For seals you pick to make up for an area you're weak in. Mp5 of some kind is always ok for seals, armor if you're scared of losing vs an ad champ in lane and if you, for some reason, aren't worried about any of those take ap/level (usually not worth it). Then for glyphs you usually want to increase your damage output overall with these. Magic pen aren't the best option for mages damage-wise. CDR glyphs are useful, but if you get the 9% from masteries and some from blue pot and potentially blue buff you may create overkill of cdr (max 40%). If you aren't getting cdr elsewhere then they are definitely useful. Also, quite a few people recommend CDR/lvl runes because they help you hit the 40% cap nicely with certain builds, but they often create scenarios where you have too much cdr or you would've preferred to have the flat benefit early. As for the choice between Ap/lvl and flat Ap, it depends on when you want to do more damage. Flat Ap will be stronger before level 6, while Ap/lvl will be equivalent/better at and past level 6. So wherever you want your damage increase is up to you. A last alternative useful glyph is flat magic resist, these will make sure you aren't destroyed by another mage in a 1v1 scenario (kinda situational). Quints are pretty much between Flat Ap and Flat Health. If you are newer to the game, I recommend Flat Health. They will make your mistakes in lane matter less as you have more health to work with. Once you become more skilled Flat Ap are fairly essential because you can usually avoid harassment while dishing out your own more potent harassment.

Personally I run this setup on most mages:

Magic Pen
Flat mp5
Ap per level
Flat Ap

See here: http://www.squidoo.com/league-of-leg...ne-pages-guide

My general caster rune page is:

Reds: Magic Pen
Yellows: Flat Mana Regen
Blues: AP/level | Flat CDR :: 7 | 2
Quints: Speed

Reasons:
Red - primary; MP > AP
Yellow - Flat versus /Level evens out ~ Level 3-6, when you really don't need the boost anymore (Items should suffice)
Blue - +1.6% CDR means that I get 10% CDR from runes & Masteries rather than 9%; need all the AP you can get; MP will only get you so far before it's wasted.
Quints - Mobility is huge on casters. 4.5% bonus movespeed (sometimes 7.5% w/ masteries) is almost the equivalent of a free half-set of boots, but it boosts movement from boots as well, so you can have MS comparable to Boots 3 w/ MP boots. Plus I got them for Christmas (when they were 1/2 off).

I just want to point out that Flat AP for Seals, Marks, or Glyphs are not worth it. The per level AP runes equal the flat runes at level 6 so after level 6 you have more AP then with just flat runes. However, the flat Quints are worth it because the the per level Quints do not equal the flat runes until about level 10-11. So pretty much all games will last past level 6, but some games could be over around level 10-11. So my recommendation to people that are reading this post is to DO THE MATH for any rune to see if you will benefit you for either flat or per level.