Hi Robin, you'll find some lovely ideas here - https://www.thekitchn.com/the-smartest-ways-to-organize-your-cookie-sheets-249532
I store mine under our stove
Flat cookie sheets, and baking sheets with a narrow edge, can be hung up with jumbo size bulldog clips.
I have mine on a shelf and I use a divider sort of like this. It works out nicely.
I store my assorted cookie sheets on top of the refrig, they are face down and very handy.
I have them in the drawer under my stove oven.