Costing is usually calculated by Products. In fact, there is also the Activity which is usually “Construction”. It is a macro level activity; sometimes we do not name it because it is obvious that we are treating the construction phase. The Products are much more detailed than the activities, that is why we say that Costing is Product oriented. Then we do Quantity estimated multiplied by the Unit rate, and we obtain the cost.
But with the 3D WBS method, we have 3 dimensions for the Work. We have also the Zones. Therefore the 3D WBS method recommends to do the Costing by taking in account the Zones. We estimate one quantity for each Zone. The result is more precise…
We can see an example below.
In others words, each schedule task has a budget (task = crossing between one Zone, one Product and one Activity).