Your pricing rules, in whatever form they currently exist; a laminated sheet on the reception desk is fine. They are the most useful artefact you have, because they are where a calendar with slots fails and where the scope of your build is really decided. Bring the exceptions too: the standing block booking that never appears in the system, the coach who is invoiced monthly, the rate nobody can explain but everyone honours.
Bring the physical layout as well: which courts divide, which share lighting or access, what cannot be booked while something else is running. Those constraints are the difference between a calendar and a booking system, and they are rarely written down anywhere.
We take these into a requirements session and a mindmap, then build a prototype on your real courts and real rates before anything is priced, so the pricing engine is corrected against reality rather than approved on a diagram. Questions that come up before that are answered on our FAQ page.