This features are not always easy to modelise. The next chapter in my 3D tutorial is about drawing a wooden side panel with an elliptic window sash.
The first step is done in Illustrator. If you are famliar with drawing in your 3D software, you can do it directly.
But I prefer make the basic objects in Illustrator:
1/ The side panel with the window cutout (yellow).
2/ The window moulding (red) and
3/ The elliptic sash window panel (blue).
I draw this 3 elements for the normal paired window and for the small simple window. The paired window panel ist 64" wide.
Saved in file format Illustrator 8, you can open this document in Cinema4D. The best way is to make each element step by step.
The side panel is made first. The flat 2D drawing is "extruded" 4.5" deep and becomes 3D. The lower part of side panel was then adjusted to the full height.
Second object to be extruded is the window moulding, with an offset of prototypical 1 inch. And the the the elliptic window is added, extruded 3.5" deep, or about 1 mm in H0 scale. This is the minimum thickness recommended for most usual materials.
Once this elements assembled and aligned, you have already a basic side panel.
The remaining parts are based on simple cubes and are made native in Cinema4D: the Letterboard, and the lower paired window. Now the basic side panel is finished.
What is still missing are the grooves.
The grooves are "cut" in by a boolean operation. They are drawn first as "positive" long strips (red). Their prototypical width is exagerated to 0.8" and they are spaced 2".
and then multiplied by clooning and carefully placed. The boolean operation engraves the grooves "negative" in the side panel.