As a Cho'Gath main it really depends on a ton of factors like how well you're doing, who you're against and what the rest of your team is made up of that factors into whether you should be building tanky or more damage.
There's not really a cookie cutter build although I favour building tanky and a bit of AD for consistent damage output if I can. I only build AP against the really bad match-ups like Riven, Malphite or Jax. --- You are now blinking and breathing manually. http://i.imgur.com/j8p5fA8.png