Well, if you like playing him more tanky than killy, go for the sapphire crystal & H pots like Kippie said, but turn it into catalyst and then rod of the ages instead of sheen. Buy level one boots over completing the rod though. Works great with your passive so you end up having a **** load of health very early on once it's complete. With upgraded boots and overdrive, it's usually enough to get you out of most sticky situations mid-game unless you screw up big time and find ALL of them alone, or somebody's fed to all hell.
Plus, if you're conservative on your grabs, catalyst will take care of a lot of mana problems for as long as you should be laning(and a little bit after you should stop, which is often the case with me. ).
Boots? Merc if they have a lot of CC. Swiftness if not. Mobility for lulz. Activates by the time overdrive's over, so the slow isn't that big of a deal. I'd still take swiftness over it.
After that, I either get Rylai's or Frozen Mallet. People get away from the grope sometimes. One of those two makes that not happen anymore. Plus, either one makes powerfist an escape mechanism if needed!
After that, it's your pick. This is around when I'd get sheen if I'm having no trouble living or something to tank better if not. I personally stick to AP after this point and get lich bane instead of tri force, but that's just me.