In pyramid forecasting, the "roll up" process begins with:

Pyramid forecasting is a method of forecasting that uses a hierarchical structure of data to improve the accuracy and consistency of the forecasts. The lowest level of the pyramid represents the most detailed data, such as individual product items, while the higher levels represent more aggregated data, such as product families or total business. The “roll up” process is the process of aggregating the forecasts from the lower level to the higher level, starting with the most detailed level. This process helps to align the forecasts across different levels and reduce the forecast error123 References: 1: Pyramid Forecasting Process 2: Rolling Forecast Model | FP&A Tutorial + Excel Template 3: ROLL-UP FORECASTS