I'm going to talk only about the cheat sheet, the actual guide is lacking a lot of stuff, like in-depth explanation of the items, runes, masteries and etc.

Apart from Abyssal Mask, your defensive items are... terrible. A good defensive item is Zhonya's Hourglass or Rylai's Crystal Scepter for example, that still gives you a lot of damage and some defense. Cassiopeia is all about positioning, if you need that much defense you're doing something wrong for sure and missing all the potential Cassiopeia has, you're the Carry, not the Tank, leave the tank items for tanks and build damage. Please, I ask you to remove Thornmail, Frozen Heart, Randuin's Omen, Spirit Visage and Locket of the Iron Solari, these are not defensive options for an AP Carry. And you actually don't even mention Banshee's Veil which is quite good against some APCs, even though it doesn't provide damage.

Rabadon's Deathcap is a honorable mention and yet you talk about it on your 2 final builds? Why not put it as a core item already, and Rylai's Crystal Scepter is quite good for Cassiopeia when chasing down an enemy, since you can spam your abilities, they won't be able to run away from you at all, in my opinion it is a core as well, so my Final Build example would be:

1. Normal Build: Sorcerer's Shoes, Rod of Ages, Liandry's Torment, Rabadon's Deathcap, Rylai's Crystal Scepter and Void Staff

2. Build against AD: Sorcerer's Shoes, Rod of Ages, Zhonya's Hourglass, Liandry's Torment, Rabadon's Deathcap and Rylai's Crystal Scepter

2. Build against ultra heavy AP: Sorcerer's Shoes, Rod of Ages, Abyssal Mask/ Banshee's Veil, Liandry's Torment, Rabadon's Deathcap and Rylai's Crystal Scepter

And the masteries, Enchanted Armor is only good for tanks that stock armor and MR, Recovery is much better for you.

I think that's what I have to say for now.