It's great to be able to reuse old structures for coops!
Chickens need LOTS of ventilation in their coops and they, being birds and not mammmals, do not need to have a heat source in the coop except in the most extreme conditions.
Your coop looks to be severely lacking in ventilation. It would be ideal if you could cut the top 6 inches of sheathing off the front and back of the coop and cover it with 1/2" hardware cloth on the inside and outside. I would also add two top hinges windows to the coop for light. Back the window openings on the inside with 1/2" hardware cloth too.
You've got a good start!
