http://www.mobafire.com/league-of-legends/build/cassiopeia-the-spellwampqueen-187258#lastcomment
Check out this build, its pretty damn good :)

Srsly....no mana issue?

thank you :D :)

great guide. had never thought about spellvamp or cassion but after a few games (and one penta-kill) i found it very usefull :)

Nice!

Thank you for all the comments so far. It is also possible to start in lane with a Sapphire Crystal i think, but i never tried it out. Usually i prefer the mobility to dodge spells and land mine easier.

The boot thing: Yep you are right. I must change it, i made a mistake in thoughts. Socerer's Boots should be preferred.

Masteries: 1. Why the hell the downvote... a little bit more content in your comment would be sth i appreciate.

2. Personally i like manareg yellows+ Meditation since i think that Cassiopeia is one of the manahungriest champs ever, but i think i said that you should free to mix the points in Swiftness / Meditation so that it makes sense to you and your playstyle ( i always play rather aggressive with cassio and take lasthits with Q and E from time to time).

3. A Hextech Revolver is imo somehow the key to win the lane with cassio. Having a Catalyst the protector will give you come basic regeneration, but a Q on the caster minions with Hextech Revolver will heal you for almost 100 HP, and i think this is something that you should not neglect. But i think i will change this item as something to buy against heavier nemies.

4. Teleport is k, i do not like it for mid (always take it on top), but i will add it to my list.

So far from my side, thank you for the comments and especially Zell ;)

I have stopped reading when you stated that CDR boots are better then Sorcerer's ... I won't downvote but just to infrom you - most of carries, your main targets, will have 30 Magic Resist and with MPen Marks and Sorcs you'll be penetrating 29 MRes leaving your target with 1 point of magic resist. Meaning that you will deal over 99% of damage instead of ~77%. So mage with Sorcs will deam around 28% more damage then one with Ionian boots ,rather big increase, eh?

Quite a instructive guide, showing a discerning down to earth approach. This sort of style will beyond a doubt assist newer players to a greater extent. To the person above me who down voted, there is only a 4 points of error in the masteries big deal? The basis of it is correct and same goes for the rest of the guide but with some parts in need of refining.

Pros / Cons

I actually think to contrary of the con regarding burst since Cassiopeia has a pretty high base health value compared to other AP mid carries and since your rushing Rod of Ages you become even more bulkier. If for whatever reason your still fearful you can always just buy one or two Dorian's Ring which work well with her.

The Pros and Cons section itself should be more directed at the champion as an individual rather with reference to the build rather then the other way round.

Runes

As far as Glyphs go for AP mids Greater Glyph of Ability Power are rather bad in comparison to Greater Glyph of Scaling Ability Power since once you hit level 6 which will happen swiftly they out surpass them. Point being, as an alternative you should include Greater Glyph of Scaling Magic Resist or Greater Glyph of Magic Resist instead, both of which provide a well amounted defense which proves of use against heavy AP burst casters like Veigar and LeBlanc.

Masteries

You'd be wanting to grab Summoner's Wrath since your taking Ignite in addition to that you shouldn't have any mana problems (as stated by your pros section) thus Meditation is trivial (you already have Greater Seal of Replenishment in order to encounter any early mana problems) and your better of with Swiftness for that edge in movement speed.

Summoner Spells

I feel you should add Teleport. Be it if your against a laner in which you feel that you would struggle against or simply to help be better at carrying your team by teleporting in lane to save them from a "oh ****" situation or to cause said situation.

Items

Yeah, I really just don't feel the need for Hextech Revolver early-game especially since you have two items in your build which take time to stack out to their respective cap ( Tear of the Goddesses & Rod of Ages. Only occasions I would consider doing so are against sustain monsters who may try to force me out of lane like Swain or an orthodox Warwick going mid - whatever it may be.

You seem to have a misconception of how Magic Penetration works and I think this had lead you to incorrectly misjudge Sorcerer's Shoes in undervaluing the item heavily. You seem to imply that if your planning on getting a Void Staff then you should get Ionian Boots of Lucidity and it will be just fine which it won't. Void Staff stacks multiplicatively thus only being of real use against people stacking heavy magic resistance typically being tanks ( Rammus and Amumu for instance). The one thing they have in common besides a high amount of magic resistance? You don't want to focus on either of them, instead the squishy high priority targets (and bruisers to an extent) are your main goal and are the ones who will most commonly not have much magic resistance besides from that of internal factors like base stats and runes or external factors like Aegis of the Legion. So, against someone who has 50 magic resistance Sorcerer's Shoes will penetrate the same amount as Void Staff but at the obvious distinct lack of cost and major gold efficiency.

Quite a nice guide. The spelling and grammatical mistakes aren't that big a deal, though I do suggest running your text through a word processor (such as MS Word) to clean it up a bit.

You might want to include some other possible starts (like the one mentioned above for early Tears), and put in some suggestions on switching item order where necessary, but other than that this looks great.

wrong masteries...

this is a great guide,but i am wondering can an alternative be a sapphire crystal and 2 hp potions instead? considering crystal builds into a tear of goddes? and shouldnt we buy tear of goddess to start charging it faster? guide was awesome!

Nice looking guide. and build. So it deserves a thumbs up :)