My hybrid build involves starting out with AP items and playing AP style...then transitioning over to add AD to help his mid to late game. I use Hybrid items due to their high efficiency.
The key is to start as AP and not to dilute it during laning so you can farm creep waves with your shield for some time and use the high burst to hoze enemies.
+ Dorans Ring - a great starter item. Health, AP, regen.
+ Amp Tome - pure AP is good stuff.
+ Meki -- more MP5 for shield spam with occasional stun.
+ Amp Tome - Moar AP.
-> Fiendish Codex -- very efficient item. Adds CDR which is nice later on.
-> Sheen -- Adds a bit of extra punch when you Stun/Boom/Autoattack.
You have +70AP and rank 5 shield which should be enough for creepfarming for a long time. It will slightly increase with 2 of your hybrid upgrades later.
+ Negatron Cloak -- You need the MR ASAP.
-> Merc Treads - Even more MR to resist burst damage which is your worst enemy.
+ Zeal - Boost speed so you can catch baddies with Stun/Boom combo.
-> TriForce - Gives him a bit of everything and the Slow Proc is very very nice.
-> Nasher's Tooth - The other side of fiendish codex. Adds AS and more AP. CDR allows faster stun spam and ensures Ult is up.
-> Banshees Veil - standard defense and health booster if needed. Otherwise skip.
+ Infinities Edge -- Standard offensive goodness.
I strongly considered hextech revolver after Sheen and then upgrade to Gunblade later. However I decided against it because after 2 of the 1200 gold items, midgame is here. Thus the movespeed of Zeal and rushing to TriForce made more of an impact over another AP item.
I also discovered that I didnt need the spellvamp since my stun/shield is an OPENER and doesnt occur much after combat.
I have a freaking ton of lifesteal with ult, so didnt see a huge need for it.
The slow/nuke is good but TriForce proc with high AS and high MS makes it a bit redundant, though I do like its tasty 700 range.