Ok, I'll try to explain based on my Gold 2 Knowledge (lel).

Penco* (AD Shaco) is not the build with the most DPS (Late-Game at least), nor the most burst, BUT it's super gold efficient because of the sheer amount of stats you get from each Item (Warrior, 3 Stats + Smite Upgrade, Youmuu's = 4 Stats, Maw = 5 Stats, Draktharr = 3 Stats w/ loads of damage), and because these Stats are so easy to get you have lot's of early game power, But these stats fall off after the 35-45min mark, but this is were more of it's magic comes from, your build does not have static components, you can always build 2-3 different items (selling Warrior ofc), that gives you utility/tankyness/stats in general.

While Critco is a scaling Build, you don't have much damage with only 1-3 Items, but after you get tour 4th-5th item going then things start to roll smoother. But as any good thing in life it has it's bad parts, you'll only start dealing damage after 4 items (as I said), and they by themselves are not that useful nor they bring utility, you'll have a ton of damage ofc, but you'll be squishie and you'll only have ofensive stats that are not gold efficient.

"When should I build Critco or Penco then sensei?"

If you feel Like the enemy comp outscales you and/or their earlt-mid game is pretty poor, Penco.

If you feel like you got this on your bag late-game then Critco.