Replace or reuse???

Howdy, I hope you all doing good. We are renovating our house and the works would probably start by next month. Before that, I need to take a decision for my roofing. Ours is a slate tile roofing and some of the slates are old. My question is, whether to replace the slates or better to use them again. My friend suggested me to replace it with new ones... What are your thoughts on this???

Is reusing the roof slates a good idea? As winter is approaching, we need to get it done fast. Does the roof color play an important role in maintaining the aesthetics of a house? Which would be the best slate roof color for a contemporary style house? Waiting for your replies and thanks in advance.