I've tested out 6+ other Morgana builds and with my own tweaking came to almost the same build as you. I think this is the best build I've seen (can't speak with regard to masteries/runes) for someone who is not a high level/high $$ player.

Unless you're playing some real squishy n00bs, I think the catalyst is better vs the soulstealer since it gives you more mana and builds towards an earlier rod. I have tried an early catalyst and end up feeling mana dry and not able to solo a lane or chase down an enemy. If playing with soul stealer, I'd say use clarity over teleport as it will give you more kills early game to power up the soulstealer.

I have not yet tried the ionian boots, but they are probably better with the catalyst and I would highly recommend the crystal scepter over the deathfire grasp. Slowing ppl down is awesome whether chasing or fleeing.