How do you perform an accurate calculation of painting expenses for a Hall Room in Winterthur, excluding ceilings, 2 doors, and 2 windows, with dimensions of 8m x 3m?

Performing an accurate calculation of painting expenses for a Hall Room in Winterthur, excluding ceilings, 2 doors, and 2 windows, with dimensions of 8m x 3m, consider costing you CHF 315.00.

*) The calculations are approximate, based on a room height of 2.4m, and include one coat of paint. The price covers only the labor, excluding any services or materials.