Thanks to everyone who contributed to this discussion. It has all been helpful
I dont think costing will be an issue. We will not need to hold costs per variant. The variants are simply a way to be able to record the in-stock quantity per size of stone (piece) and to be able to translate between pieces (variant quantity) and area (the base unit of measure) while avoiding the need to hold different items per size of stone.
I am hoping that I can do something simple like associate a UOM with each variant which will convert from pieces to the base UOM (e.g. square feet). Then when processing orders, journals ,etc the operator will be allowed to enter the quantity as the number of pieces (the variant UOM). This will be converted to the ‘Quantity’ field in the base UOM for the item.
The user intends to use lot numbers (correspondng to pallets in the real world). When we come to sell we may be issuing several variants to supply a single order line. I havent worked out the best approach to this yet.