I like your build up to lvl 10, at this point its debatable between upgrading tower or hammer.  And boulder roll lvl 2 should be considered once hammer is up.

Also all rooks should take crimson vial as their favor.  Its just so money late game when you are being focused that you need to heal up fast. 

For items carry teleport scrolls, a sigil (which double stacks with crimson vial is super!) and ORB of defiance.  This will wipe away spits, and help you survive being focused while the cavalry (your teamates) arrive to save your ass...

For armor, just health stack.  start with banded armor and the 1st helm.  Then get unbreakable boots, nimoth chest, and the other 600 health +10 hps chest.  Then get vlemish or if u have the gold hungarlings.

This is pretty similar to what I do as rook.  Crimson is the way to go though imo.  It enables you to stay in a lane a very long time once you get used to how to use it right. 

Vial takes some practice to use correctly. You shouldn't ever get your vial interrupted, but, the added advantage is that people will try, which means you're more likely to escape. Vial is a 1.0 sec cast. With boulder roll I (0.5s stun) you can almost always get it if the person is at a distance or if there is lag. With boulder roll II you can always vial safely.

From the very beginning vial will heal you for almost/around 800 health, so it's pretty much as good as vial at the point minus the 5 hp/s.

Staff of renewal is a much more fun favor item. Staff lets you put up more towers, stun more often, and hammer more often. But you will definitely need two helms. I usually get my second helm before level 10. At level 10 towers cost only 200, which cuts down on your mana cost. But as you level up hammer slam, you'll need that second helm.

There is a huge difference between slamming once in a fight and slamming twice in a fight. The rook who slams twice will win the portal. This rook is also putting up 20% more towers during that fight