Hello, welcome to my Morgana guide
i hope you try it and i hope it works ;)

For runes i get :
Mag. Pen. marks
mana regen seals (so you don't need clarity)
and Mag. Res. glyph (good against an other AP-champ mid early)
and flet AP Quintessence (good for early domination ;p)

start with Doran's ring for health and mana regen
than get your catalyster (maybe one or 2 hp potion, but not necessary) for mana and hp
afhter get boots of speed, go then or sorcerer's shoes or first Rod Of Ages (i prefer first Rod Of Ages) then i get Hourglass (for little armor and AP) next Rabadon (or first Rabadon and then Hourglass, if you get kills go then maybe first for Rabadon ;) )
after that Void staff for more AP, then you can get a Banshee or more AP or somethings Armor but last item you can chose in the game (watch enemies, more armor? more mag res?)
PS don't forget the passive of Housglass, you're invulmerable for 2 seconds, can use it by malzahar ulti or in a teamfight

Try with spell vamp in combo with Tormented Soil to get more hp and farm

one more tip :
When you snare the enemie with Dark Binding, pull under him Tormented Siol for more dmg (and spell vamp)