Step 4 : create the wall plate (in a new body)

Note: In reality the wall plate is built in seven parts assembled together, but the objective of this tutorial being to show how to use external pilot parameters, it will be built here in a single block.
It's up to you to detail it if you feel the need.

In this new body, create a reference plane from the XZ plane.
Its position in Z (the normal to the starting plane in the local reference frame) is

        <<SketchOpening>>.constraints.WallHeight

In a new sketch created in this plane and after making the "SketchBase" 
master sketch visible, create the necessary geometries.

Create an extrusion with a length equal to

        <<SketchOpening>>.Constraints.SandpitThickness

Create a peripheral chamfer respecting the slope of the roof,
whose dimension 2 is 15 mm and dimension 1

        tan(<<SketchRoof>>.Constraints.RoofAngle) * 15

In a new sketch created in the XZ plane and after making the "SketchOpening" 
master sketch visible, create a carbon copy of this master sketch,
and then adapt it as needed.

Create a pocket across everything (on the right side!).