A BOM is must needed before purchasing cable trays. But it is not easy to confirm quantity of bend, tee, cross, reducers, raisers, especially for big projects. Contractors need to customize these parts from manufacturers before project start. Still changes might be occurred during installation.
Using wire mesh cable trays will not have this issue. Bends, tees, crosses and other junction parts can be easily formed from basket cable tray straight sections only with a cutter.