Uber Tier Characters: House Rules for levels 11 to 20

From publisher blurb: While the D&D Gamma World game only allows character advancement to level 10, the related Dungeons & Dragons game goes up to level 30 in three tiers: Heroics (1 to 10), Paragon (11 to 20), and Epic (21 to 30). These house rules expand D&D Gamma World to level 20 by introducing the Uber Tier (11 to 20).