I always play on crucible (I think that was the name, the 2 v 2 lvl that has only 1 lane and a flag to its left) and set up a farm in the middle of the lane. There is also a problem which I always have when using the Rook - I can't capture the gold mine flag without leaving the fight, letting the enemy DM attack the permanent towers. Same goes for the xp flag to the left. The enemy is just more mobile, and I can't keep both flags up without leaving the battle permanently. How do I counter this?
the other maps that are more popular have multiple lanes and you will also lose the speed battle. Try to get a solid hold on one lane, push it back and kill their towers. As this is a team game, the ability for you individually to hold the entire map should not be possible. you will need to rely on your team.
Another problem comes from fighting TB. The computer always comes to me and casts flame ring, which is enough to drain my hp rapidly. I usually invest into mana items, to be able to erect towers all the time, which I use both for healing and attack. However, a TB in the fight usually means crazy DPS against me, and when supported with minions to soak towerdamage - a quick kill.
for all DGs i would not suggest fighting TB in his flame circle unless you are confident you will get the kill.
also decent players will attack with the creep wave to bring down your towers, having qot's aoe spike will lower their armour so much that they will come down in 3-4 hits to a decent levelled DG
the chaining effect of the towers is simply an animation and afaik doesnt change the damage.
the godly strength is okay, but the passive damage increase can be made up for with an item or two, not to mention that by the endgame that 50 (godly strength) damage is not going to be all that significant in comparison to the damage you are doing. the boulder rolling stun is probably much more useful.
stacking mana items to allow you to build mana towers will do only that, allow you to have many towers. your strat will be useless if someone is able to effectively counter your towers as the AI TBs are doing (by either killing them or killing you/forcing you away. for rook try to stack hp and hp regen as well as a bit of mana and some armor. you want staying power to be able to fight along with your towers for as long as possible. remember you are much slower than all the other DGs and getting out of a battle can be very difficult, you want to pick your spots carefully and the battles even moreso.