My current build for Morgana is as follows:

9-0-16 masteries, getting imp. teleport and clarity.

Red Mpen, yellow mp/5, and blue cd/level

Starting items:
Sapphire Crystal, Mana pot, Healing pot

Assuming I solo mid, I get Tormented Soil, followed by:

Binding
Soil
Binding
Soil
Ult
then leveling both to 5, getting Black Shield faster if needed.

Further item build:
Catalyst ASAP
Sorceror's Shoes
RoA (sometimes before boots if I have enough gold to just buy it and I am not running around that much)
Void Staff
Abyssal Scepter if they are stacking mresist
GA or something silly if the game lasts this long.

GA is actually surprisingly nice in 45 minute plus games, because I can usually run in, ult, hit all 5, "die", then help mop up the mess.

Laning strategy:
I get Soil first to just stay behind creeps and farm. At Rank 3 it kills ranged minions in one cast. If i get the chance, I bind and soil my opponent. Once I have ult, I just use it with binding if I get the chance. Pretty standard stuff actually...

I tend not to get Mejai's because it seems to curse me to failure.

So: Are there any problems with this build, or is it all-round solid? Any discussion/thoughts on how to improve it?

It's pretty solid, IMO, except that I'd highly recommend taking one level of Black Shield before you hit 6. Also, Zhonya's is a great item for her, especially if you get it early.

no CD reduction? I'm assuming you're taking golem buff?

I would get Zonyas since its works like GA.

Hmmm i kinda try to balance my build with morgana.....deathfire grasp is sorta useful since it gives a free nuke, cd reduction and AP. Combine that with frozen hearth and you got max cooldown reduction. I usually end up liking boots of mobility on her.....Watcher her run like a mad woman in that skirt always entertains me.

Anyway your build is good but try to add something that will make her a little more harder to kill.

When you say 9-0-16 masteries, I'm going to assume you're not level 30 yet.

Max Binding first. Learn how to farm without Tormented Soil, because Binding is a great spell for harassing.
Secondly, while RoA is a good early item for all casters, I prefer rushing Zhonyas for the active ability while using your ult.

Thanks for the advice.
Shonya's + ult is just.... wow.
I will probably get Zhonyas after Void Staff if they don't have much mresist, or possibly before if boots are enough mpen.
Also if they aren't stacking mresist, I might get mobility instead of sorcerors.

And yes, I am only level 25.

Start with Dorans ring and get a Catalyst, soulstealer+boots, RoA, Rylais, Zhonyas Abyssal scepter/Voidstaff. Get lvl 1 binding and Ult>Soil>binding/shield whichever is necessary. 1 shield pt early on