Up in my ancient open shed has since before my time sat an equally old shelving unit, on which I would keep tools and materials related to a time when I was more active than I am now. So, on the very top has sat for ages an empty metal basin which I used to drain sump oil from my ride ons.
I just noticed the other day that some enterprising bird had filled it with twigs and leaves to make a good size nest, out of the weather, away from predators, except rats, though they'd be more interested in the baits I nail up on the studs.