How to add a new material layer to existing wall or Roof?

edit

Terms like workspace and measure are typically associated to OpenStudio. Without writing a completemeasure.rb file, the key bits would look something like (an example):

# Isolate an existing material, or (here) create a new one:
material = OpenStudio::Model::StandardOpaqueMaterial.new(model)

# Isolate the existing layered construction (e.g. "c1"):
construction = model.getConstructionByName("c1")

# Cast it as a layered construction:
construction = construction.get.to_LayeredConstruction.get

# Assuming "c1" is a 3 layer construction:
#   - "cladding"
#   - "sheathing"
#   - "finish"

# Insert new material after "cladding":
construction.insertLayer(1, material)

The function insertLayer is documented here. To first edit the material, rely on functions described here.

If instead strictly interested in editing an IDF file, e.g. simply insert the new material as 2nd layer:

Material,
  insulation, !- Name
  Smooth,     !- Roughness
  0.075,      !- Thickness {m}
  0.05,       !- Conductivity {W/m-K}
  785.0,      !- Density {kg/m3}
  830.0,      !- Specific Heat {J/kg-K}
  0.9,        !- Thermal Absorptance
  0.4,        !- Solar Absorptance
  0.4;        !- Visible Absorptance

Construction,
  c1,         !- Name
  cladding,   !- Layer 1
  insulation, !- Layer 2   <<<<<<
  sheathing,  !- Layer 3
  finish;     !- Layer 4