Italy (and others) could (and should) do both.

Only thinking in terms of cost is short vision IMO. What happens if in 20/30 years you need to dramatically ramp up the energy generation (maybe everyone will drive electric, maybe house heating will be electric, maybe someone will come up with a new tech that requires a huge amount of energy, ...) and you already covered most of the roofs? or panels and batteries are at their end of life and you need massive investments just to keep up with the status quo?

I woulnd't go in a fight with a fist tied behing my back, and global warming is one of the biggest fights we must face.