I feel that it is a bit dubious to save 3 levels worth of points. Usually, by level 14, the game is already decided (if not over). You won't get to level 15 in general as rook (although, if you do, your slows will be epic). You could easily throw a point or two into towers without sacrificing too much. I tend to think that a Hybrid Rook is the best. Also, this build seriously sacrifices ganking potential. Here's a replay:
I made some stupid-ass mistakes, sure, but in general, Rook's towers made ganks happen that would not have happened otherwise without the towers. One of the best strategies I've seen is throwing up a tower in enemy lines. You force your opponent to deal with the towers or risk being ganked. They didn't deal with the towers, so they got ganked by a UB, which is a fate worse than death.
I will say that a strength of your build is low mana usage. Rook crucially needs armor, and your build can afford it since you don't need two mana helms.
My suggestion: Try throwing in a point on towers at level 1. If you don't want to delay your build, forsake Trebuchet until after level 12. One point in towers is good early game and late game. On the downside, you won't be able to afford as many hammer slams early on, but towers are more powerful at level 1 anyways.