Level (-2) All Owner Jobs (To the Owner "The mother of the Whole")
Level (-1) Owner Jobs by Municipality
Level 0 Individual Owner's Job
Level 1 All Contractor's Portfolios
Level 2 Individual Portfolios
Level 3 Jobs By Continents
Level 4 Jobs By Country
Level 5 Jobs by Municipalities
Level 6 .... whatever gets down your pants
Level 10 Whole Project
Level 11 Zones or Sections
Level 12 Workfront summaries under Level 2
Level 13 Task Cascades for each workfront
Level 12 Individual tasks
I see the pretentious of some to define a "Universal" self serving definition of levels quite stupid. It shall means different to many, depending on your needs.
I use several WBS definitions for a single job, each with different levels, this complicates the above myopic vision.
P.S. If negative float is not an erroneous concept I guess negative level is not.