This will completely depend on what information your supply chain needs to act on, what informs their decisions - go and ask them what information they need to do their work! Working with supply chain in the past we've had KPIs ranging from:
Stock Value
Stock Days (a measure of how long the current stock would last given average volume of sales)
# of Product Lines stocked
# of Credit Notes issued (due to stock not being available)
How you create them depends on how your audience consume information. Some of these I created as gauges (as in % of picks that caused a credit note), some work just as a number with an indicator to show a comparison (Stock Value vs Stock Value last year - are we holding more stock? Does that tie in with a sales number?) And some I've shown using images or one expression bars. This all depends on what you are measuring, and how you can both simply yet effectively portray what they need to know about the information.
