It would probably depend on the lane. Haunting Guise is a nice early pickup due to it's cost efficiency, cheap components, and good early-game stats. Afterwards, you could easily build Frozen Heart or Sunfire Cape against AD opponents or Abyssal Scepter (or Spirit Visage or Wit's End) against AP opponents.
Tahm Kench seems like he would scale primarily off of magic penetration, CDR, and defensive stats (primarily health, resistances secondary). Since his abilities have low AP ratios but high base damage (including a massive percent-health damage ability), building penetration and lowering his cooldowns seems like it would take advantage of his strengths.
This was mostly just me brainstorming though; I've been waiting for Tahm Kench to go on free week so I could try him before deciding whether or not I wanted to purchase him.