[MoonWitch]

local frame = CreateFrame("Frame", "Bob", UIParent)
  frame:SetPoint("CENTER",UIParent,0,0)
  frame:SetSize(100,100)

You can just use self, since a frame to hook into isn't needed, oUF handles all that.

-- Register it with oUF
  self.Health = Health

The Self.Health is a reference to self.Health from oUF itself, in that part you're telling oUF that the frame you called Health is self.Health from oUF. Otherwise oUF doesn't know what to do with it.

And this should purely work...

------------------------------------------------------------------------
-- oUF Layout boiletplate
-- Author : Kelly Crabbé
------------------------------------------------------------------------
------------------------------------------------------------------------
-- Namespace
------------------------------------------------------------------------
local _, ns = ...
 
------------------------------------------------------------------------
-- Config
------------------------------------------------------------------------
local NORMALFONT = STANDARD_TEXT_FONT
local TEXTURE = [=[Interface\ChatFrame\ChatFrameBackground]=]
local BACKDROP = {
  bgFile = TEXTURE, insets = {top = -1, bottom = -1, left = -1, right = -1}
}
 
-----------------------------
-- Add custom functions (overrides)
 
------------------------------------------------------------------------
-- UnitSpecific settings
------------------------------------------------------------------------
local UnitSpecific = {
  player = function(self)
  -- player specific stuff
  end,
  target = function(self)
  -- target specific stuff
  end,
  party = function(self)
    -- party frames
  end,
  boss = function(self)
    -- boss frames
  end,
  arena = function(self)
    -- arena frames
  end
}
UnitSpecific.raid = UnitSpecific.party  -- raid is equal to party
 
------------------------------------------------------------------------
-- Shared settings
------------------------------------------------------------------------
local function Shared(self, unit)
  self:SetScript("OnEnter", UnitFrame_OnEnter)
  self:SetScript("OnLeave", UnitFrame_OnLeave)
 
  self:RegisterForClicks"AnyUp"
 
  -- shared functions
  -----------------------------
  -- Health   
  -- Your Health Statusbar
  local Health = CreateFrame("StatusBar", nil, self)
  Health:SetHeight(50)
  Health:SetStatusBarTexture(TEXTURE)
  Health:SetPoint('TOP')
  Health:SetPoint('LEFT')
  Health:SetPoint('RIGHT')
 
 -- Your health background, not needed but handy to see
local Healthbg = Health:CreateTexture(nil, 'BACKGROUND')
 Healthbg:SetAllPoints(Health)
 Healthbg:SetTexture(TEXTURE)
 Healthbg:SetVertexColor(139/255, 70/255, 70/255)
 Healthbg.multiplier = .75
 
  -- Options
  Health.frequentUpdates = true
  Health.colorTapping = true
  Health.colorDisconnected = true
  Health.colorClass = true
  Health.colorReaction = true
  Health.colorHealth = true
 
  -- Register it with oUF
  self.Health = Health
  self.Health.bg = Healthbg
 
  -----------------------------
  -- Power
  -- Your Power Statusbar
  local Power = CreateFrame("StatusBar", nil, self)
  Power:SetHeight(50)
  Power:SetStatusBarTexture(TEXTURE)
  Power:SetPoint('TOP')
  Power:SetPoint('LEFT')
  Power:SetPoint('RIGHT')
 
 -- Your Power background, not needed but handy to see
 local Powerbg = Power:CreateTexture(nil, 'BACKGROUND')
 Powerbg:SetAllPoints(Power)
 Powerbg:SetTexture(TEXTURE)
 Powerbg:SetVertexColor(139/255, 70/255, 70/255)
 Powerbg.multiplier = .75
 
  -- Options
  Power.frequentUpdates = true
  Power.colorPower = true -- powertype colored bar
  Power.colorClassNPC = true -- color power based on NPC 
  Power.colorClassPet = true -- color power based on pet type
 
  -- Register it with oUF
  self.Power = Power
  self.Power.bg = Powerbg
 
  -- leave this in!!
  if(UnitSpecific[unit]) then
    return UnitSpecific[unit](self)
  end
end
 
oUF:RegisterStyle('Bob', Shared)
oUF:Factory(function(self)
  self:SetActiveStyle('Bob')
  self:Spawn('player'):SetPoint('CENTER', -300, -250)
  self:Spawn('target'):SetPoint('CENTER', 300, -250)
end)