Follow the guide when it works and sell the doran's ring when you've gotten a few items. Obviously don't get a mejai's if you're not doing good, get a haunting guise instead, it's a great replacement. Or you can just skip the mejai's all-together. The morello's tome is absolutely necessary as Morgana has high cooldowns compared to most other mages. If a game lasts long enough to get a lich bane then you probably need it. Lich bane really helps with pushing as you'll be able to hit several hundred on a turret.

Dark binding is your main attack. Use it to initiate and help your team. When u think a stun will hit be sure to place tormented soil down for that extra DoT. Shield is pretty self-explanatory :p. As for your ult, useful for a spell combo going dark binding, tormented soil, soul shackles, that way you get the stun shortly after they can move.

-Also if the enemy is caster-heavy grab your shield early if you need to and upgrade it when necessary.

Ignite- Very useful for Morgana as she has a DoT and it helps her get that easy kill while your target is immobilized.

Clairvoyance- Better for pre-selected teams, but i love it none-the-less. Helps check baron, dragon, or the brush for enemies. Sometimes I use it to gank the enemy jungler.

ALTERNATIVEs

Teleport- If you usually have problems staying in lane because of harass, then get teleport so you can get back in lane fast.

Heal- I wouldn't suggest this because of Morgana's passive spell vamp, but it's useful if you have issues suriving.

Cleanse- What can I say? It's an awesome spell, I personally always forget to use it :p, but still very useful.

Flash- Great spell for survivability and useful for keeping up to someone you shackled for the stun and extra damage.

-Anything not listed here I would not suggest at all for reasons I'm too lazy to mention.

Morgana can farm quickly with tormented soil, so use it, just not so often that you have mana issues. Immobilize enemies that will die between you and your team when they over-extend.

I personally don't play Morgana mid very often, if possible leave mid to someone like Miss Fortune or Ezreal when possible. Still though fairly basic, farm minions and harass the enemy, try to keep them away from the experience.

Hopefully I can update this guide soon and get some screenshots of an average game to show how good this build is. Also I've been meaning to try dps morgana more, as I did one game and went 17/2/8 :D.

Seriously try the build before rating and go nuke some people :D.