One suggestion, check out the threads from the Alaskans'. They have some really great posts and lots don't heat their coops, even in their terribly cold environment.
One thing I have learned is that ventilation is paramount and if done right, will prevent the frostbite.
It seems that the moisture is the problem, more than the cold is. Having the right ventilation, that will help get rid of the moisture the chickens produce, will help even more than heat.
One thing I read and it made sense to me was; if you heat your coop, in a northern cold climate, and the electricity goes off....chickens will die with the drastic temp drop. Their bodies acclimate to the winter temps and with the correct ventilation. They have feathers and lots of down too!
I have read post after post of OP's from Alaska, that have no problems with the cold and don't heat their coops. The bantam's are more fragile, so not sure on them and heat, and that brings up another thought.
Picking breeds that are cold tolerant is a must for those of us that live in the northern regions.
I agree on the heat lamps also. MOST coop fires are in the late fall, early winter, as people attempt to "heat" their coops with the heat lamps.
Just some food for thought !
Sooo sorry about your Roo
Poor guy!!!!