Depends on opponents makeup. Get your regen pendant, go to lane. Early build usually looks like this for me:
Rupture or Scream (Rupture if likely to get a kill or being pushed hard)
Rupture or Scream (Scream if I don't have it yet)
After that, Feast > Spikes > Rupture > Scream. If I'm getting badly, badly out-ranged by opponents, I'll move rupture up above spikes - to destroy creep waves from afar.
If you have a great gank setup, conserve mana and go for it. Typically I don't get a lot of early kills on Cho against a decent team. If you're facing a smart team, the strat I've used is to rupture the creep waves - hit as many creeps as you can. Then wander in with spikes and collect cash. Remember each creep kill is +health for you (passive), and wandering over to kill them you will likely have a chance to hit enemy heroes with spikes. I play head games, mainly - I act with my rupture and spikes like I'm going for the heroes, but I'm really farming minions - it keeps me at full health and earns me cash.
Feast for pushing: Early game if there's no chance of a gank in my lane, I feast the big cannon minions that come every few waves. You want to have 3-4 feasts up quickly regardless, so don't hold on to it forever hoping for a kill - get those free HP.
Time to take stock. What does your opponent have for damage? You have four concerns as a tank: HP, Armor, MR, and *movement speed*. Cho's spells are relatively cheap, it's hard to run out of mana with him if you play conservatively. I haven't bought mana regen in ages.
Typically, my priorities for early game items regardless are: 1 +HP (ruby or giant) && 1 Boots. These get upgraded as follows:
Boots: Ninja Tabi for melee (and are very cheap with terrific stats, upgrade quickly if this is a good option) or Merc Treads for MR & snare resist. Higher games I normally do the latter.
Warmog's: This is a priority item. Earlier you get it the better.
Zeal: I usually pick up Zeal for +8% movement, +attack/damage. I have outrun opponents a number of times - movement speed is a huge advantage. The extra attack speed also helps wipe out creep waves and helps down towers later. This is usually my first 'side' item after the two core items.
Armor: I could write an entire sub post on this. It really depends on your opponents -- if you need MR or Armor, and whether you are likely to see a lot of team fights. I typically pick up more armor in one fashion or another next before goign for more health. Aegis of the Legion has become a favorite mid-game item as it is quite versatile and team-benefiting, and somewhat cheap.
Atma's impaler is a priority for late game for me (16+) because with it and Zeal I start to stand a decent chance of taking down towers. At that point I might look into upgrading to Phantom Dancer as well.
I've never seen the point of sunfire cape - Cho's auto-attack spikes do more damage.
Cho's role to me late game is lane control. If you're being pushed back to your base, he can rupture -> scream -> attack once and wipe out an entire wave of creeps (or nearly) which means your tower will auto-target the next hero it sees. This can be quite a deterrent to enemies intending to storm your base.
On the flipside, if you get an atmas and phantom dancer, you can tp to their base and wreck a tower. I've teleported from my base as they're gathering outside to a creep wave attacking their inner towers and gotten it to 50% before they arrived... and to 0% at the same time they killed me. Cho's rather tough! That gave my teammates time to come back to life and cost them one of their inner towers - we won about 10m later.
Anyhoo. I love Cho, strong early, fades a bit late the way I play him but he's always a dominant force for pushing/countering pushes.