Z Size Controls

Sets the Z sizes of the object. The object is created centered on the origin. The extrusion begins at Z=0 with the base hanging below. +Z sets the size of the extrusion, -Z sets the size of the base, add them to find the final object size. You can create an extrusion that hollows out the base cube by setting +Z to a negative number. However the results make no sense unless the magnitude of -Z is larger than that of +Z.