Staging areas may sometimes be included or not included as part of the unit size and this will also depend on the location and type of the particular warehouse. If the staging area is not included as part of the unit area, the tenants would not have to pay any additional rental for the staging area even though the tenants are benefiting from this space. However, you may note that it may sometimes also be included as part of the floor area.
While staging areas may be useful, you may note that not all warehouses have these staging areas present and it would depend on the specifications of the building and how it was built.