Gross square feet floor area means the sum of the gross horizontal floor areas of a building measured from the exterior face of exterior walls, or from the center line of a wall separating two buildings. In cases where no walls exist, the gross horizontal floor area shall be that area covered by the roof excluding two feet on each side of the structure for a standard roof projection. Outside areas used for sales and/or display may also be considered (e.g., plant nurseries, building materials, auto sales, wine production, etc.) when the planning director determines that the use of the outside area significantly contributes to the employee density of the building. For purposes of the requirements of Section 15.94.050, the square footage of any tank or wine crush pad or similar non- walled wine related structure shall be included in the gross square feet of a non- residential development project.