Best tower Rook by Obscen
PoT I
Arrows
Save
PoT II
ToL + Boulder Roll
Slam I
PoT III
Trebuchet
Slam II
PoT IV
Slam II
Slam III
Slam IV
Boulder II
Whatever
Reason: Hold lane (HP flag on cata), XP up. Late game, fighting you in a tower farm is fatal vs your Boulder Slam. You can often 2vs1 at level 13+ in your farm.
Situational Stuff
Favor 3vs3+ BotF: Exception: Enemy Rook or Reg, and you have a general on your team that attaches a monk, then you take Crimson Vial to control lane vs enemy Rook or counter Snipes.
Favor 2Vs2: Crimson Vial, holding a lane 1on1 or 2on2, crimson vial is stronger on Rook then BoTF. Especially later when you sigil and then vial.
Treb @ level 8 is amazing in good games, always the level 8 choice eg: Chances are you cannot safely push the gold towers on Cata by yourself, but trebs will take them out while you lane safely for XP while controlling the HP flag.
Warning. Doesn't matter how good you are as Rook, you need a good support team. If you get caught in a 2vs1 or 3vs2 against people who know what they are doing, you are going to die when things are equal if there is no inbound TP for support. I've died many times as tower rook to a strong push, as well have killed many good players with a strong push against their rook. When you yell HELP, you better get a teammate inbound or you will start feeding the enemy.
On the flip side of the coin, when things aren't equal, Rook can be godlike with higher gear. 10K+ life on a sigil and 2000+ uncounterable damage? Real hard to overcome.
Another problem I've noticed with this build: You must get some time to lane alone before level 10 once your farm is setup. If you constantly have a backup DG in your lane, you are going to be level 7-8 and the rotating enemies will be level 10. This is catastrophic.
Awareness: When your tower farm is setup, Do not be afraid to TP in to boulder a 1vs1 fight when the enemy is about to need to withdraw. This will allow your teammate to chain stun for a kill.
Weakness: Occ rapes this build. You need to go hammer Rook vs Occ.