The number to watch
Actual cubic metres against ordered cubic metres per site. A pour that overruns is normal; a site that consistently overruns by ten per cent is either a specification problem or a measurement problem, and either way you want to know before the builder queries the bill. Recording every delivery against its site makes that a lookup. The same record is what your customer's engineer will ask for when the project is closed out.
Grade is the item
M15, M20, M25, M30 and their variants are different products at different rates, and a bill that says "concrete" invites a query. Holding the grade as part of the item means the rate is right automatically and the invoice states exactly what was supplied — which matters more here than in most trades, because the grade is a specification the builder's engineer signed off on and may be asked about later.
Pumping, waiting and the charges nobody quotes
The cubic metre rate is only part of the bill. Pumping, additional pipeline, waiting time beyond the agreed window, and a night pour all carry their own charges, and every one of them is a dispute if it appears as a lump sum. On separate lines with the quantity stated — hours waited, metres of pipeline — the bill explains itself and gets cleared rather than queried.
Site-wise for a builder buying across projects
A builder is one party with several sites, and the question that comes up at month end is always how much went to which project. Recording every delivery against its site means a single ledger can be read whole or filtered to one tower, which is exactly what the builder's own accounts department needs before they will release payment. Attaching the delivery challan to the invoice keeps both together permanently.