This is by no means law. This is how I like to Roflzerg with Morgana, and I hope you'll enjoy
Roflzerging too.
Hi,I'm Pridezx,and I'll be your overly nerdy guide for today.
This is my guide to Morgana for the less serious, normal / low ELO games.
I find it to be quite effective and adaptable build, I'd appreciate you give this a read before going on to follow my build to the ground.
Enjoy :)

This is pretty straightforward.
For the Marks I take Magic Pen, Cause, Magic Pen is always going to be awesome. Unless you've got Fiddlesticks and like 4 Abyssal Scepters...which I wouldn't really advise..but yeah Magic Pen Marks
Seals I take my AP, Because AP on Morgana makes you a Goddess.
Glyphs I take CDR...but most people say Mana Regen works good here too. A Personal Choice.
And Ofc AP Quints :D
Simples.

This is a Build that I would use for a Carry Morgana.
The Damage is nice, you get your 10% MP, Some flat ap, and a lovely 6% damage increase.
HOWEVER.
I find if you're playing Solo Que, I would veer more towards utility.
More starting Gold = Pots /w Dorans Ring.
More Gold Over Time = Expensive Build slightly price nerfed.
Spell Vamp = Such good synergy with your Passive and WoA, I end up with nearly 60% SV, Getting 400hpish back from a successful bind, ridiculous amounts off my ult and soil also.
But again it's a choice.

Start off with your Dorans Ring.
If you got extra starting gold pick up a Hp Pot too.
Morgana is an outstanding solo laner, please play her solo lane.
If you find that you're being harassed hard early game, Buy another Dorans Ring, it's a quick boost to alot of vital stats. You'll find this helpful in counter harass.
After Dorans I go straight for Catalyst, this item is ridiculously important for both survival and lane uptime due to mana issues, I'd go for the Sapphire Crystal first to boost my mana...which is quite clear....
Get your boots next, makes those skillshots so much easier to land, also helps for keeping in ult range if you're up there yet.
Next get your Rod of Ages, The Earlier you get this, the more prominent the bonuses will be.
If you feel you can manage without the boots, go straight to RoA from Catalyst, as this will upgrade passively, meaning that you bind a guy, he judges the damage he can take, then 4 seconds later your RoA gives you another little boost, guy thinks he can get away and boom he's underestimated our ohsopro fallen angel.
Magic Pen boots, so you can Penetrate them. Simples.
Here is where my build begins to variate from the more popular Morgana builds I've followed, again this is not intended for High Ranked Play. It's a tanky ap carry goddess of destruction, nothing more.
I get the Hextech Revolver here, it's got a nice amount of AP, and you will really notice the Spell Vamp (However I would also like you to keep in mind NOT TO BUY THIS, if you think there's a Fiddlesticks or Soraka or such thats going to build WoA, as it's an AOE buff that doesn't stack, wasted gold.), It stacks so well with your passive, I reach 60% SV as mentioned above so it's really worth it.
The Glorious Soulstealer next, for 1235 gold you are looking at 180 AP (Before the Deathcap boost) and 15% CDR, if you're not dying all the time (Hence the SV. If you can stack this to 20, you will break the other team. I reached 1000 ap with this and trust me, they will weep.
Upgrade your hextech to WoA after this, then save up for the Almighty Deathcap, if you've already got 10-20 stacks, you will really notice how great soulstealer is, 20 stacks = 160 ap.
30% of 160 = 48 ... that's 208 Ap from the stacks alone...not including the 20 (+6.75) from the actual item passive.
If you have no defensive problems WHATSOEVER, take Deathfire Grasp for that little extra bit of ...umph. However, if you're having issues popping your Ult, take Zhonyas Hourglass, getting
owned by AD carrys? THORNMAIL. I can't stress how hard that shuts down AD carries. Abyssal Scepter is nice for Magic Resist if you're getting lolwtf'd by ap carrys. I cannot stress how important it is to adapt the items to combat enemy team setup and to synergize with your own team.

Dark Binding is a great spell, excellent harass, excellent for catching an opponent or holding them down for your ult. I max this by Level 9.
Tormented Soil works well with Dark Binding, as it reduces magic resist, and it also does some nice extra damage, Dark Binding then Soil straight after = nice damage.
Black Shield was nerfed hard, however it still is a great spell, absorbs some magic damage..not much but meh...however it blocks a CC..which is kinda op. Great for Blocking Ashe's Ult or any AOE Slows or such :)
Soul Shackles...Wow..Its an amazing Ult, You should gank viciously with this Ult. It's also helpful for gaining control of that pesky harasser who's been annoying you for all early game...BIND SOIL ULT IGNITE GG :D

Flash in my opinion, is a required summoner spell, end of story.

Ignite is epic, seeing as Morgana seems to lack that last bit of damage.

Exhaust is also an acceptable choice...:P