I tend to play Rook in a similar fashion but instead of getting armor early on I invest in the gold upgrades at Cit and save for Bulwark of Ages and Belt of Giants, the cleave ability makes Rook dominate the creep/minions.
Well a point in God's Strength gives him a splash knockback on small units. That or he gets it some other way.
Don't much like Rook for killing creeps tho, other chars are much better at it. QoT, Torchbearer, UB. Those are the 3 best.