Returns the maximum extent of the object in the X direction, this can be combined with GetObjectSizeMinY to determine the size of the object in the Y direction. Note that the object may be off center so its min value may be 10 whilst its max value is 12, meaning its size is 2 units in the Y direction. This command takes the bounds of all meshes that make up this object, to check the bounds of a single mesh use GetObjectMeshSizeMaxY.
float GetObjectSizeMaxY( objID )