Everyone else seems to favor the dark binding first but I like to start off with tormented soil. I start off by placing it underneath the minions so I can rack up some easy levels in the beginning. I get dark binding second so I can pin my enemies over the soil. That allows me to get first blood, or to get ahead of my opponent. Morgana is usually mid due to her distance but she is a little low on speed and health so you have to be careful of getting ganked. I like to play her with a partner so I can snare them and 2v1 a kill. Usually I can get both lane partners that way.
This build allows me to play her strong and have her abilities do massive damage.
READ THIS!>>>After I have filled all six item slots I trade the Will of the Ancients with Hexteck gun blade and Doran's ring with Rabadon's death cap. I get guardian angel so when I get in a tough time I have "extra health" to escape.<<<READ THIS!
Teleport and Flash are always good choices for her, as well as heal and clarity. Any combination if these four summoner spells are great for her. Flash and teleport are great because Morgana is naturally slow. Heal and Clarity to give you an extra "boost". I like to get clarity so I can cast spells and gain her natural spell vamp, and with the spell vamp from the items, heal usually becomes unnecessary later in the game. Just experiment with them and see which ones you like with her.
I prefer to stick with tanks or other snaring, stunning, knock back champions, it makes it easier to escape or fight, depending on the situation.