So now that I have actually looked at your files, it looks like you are trying to replicate the 2d drawing?
To make rectangles fit within, or relative to, other rectangles you can create reference points from, for example, your main outer wall rectangle or reference points that all your rectangles are referenced to.
You almost do this here…

…where you use the Vec component plugged into the Origin (O) input of the XZ Plane component. It should actually be a Point XYZ not a Vector XYZ and instead of a Point XYZ that you set with sliders it could be a point that you have extracted from somewhere else (like the bottom left hand corner of the outside walls)
I’ve added a simple example of how to have 2 rectangles inside the outer wall rectangle that are all related…
window try mjh.gh (16.5 KB)
You can see that the more you develop this to add more components all referencing different things then the definition gets really complicated and hard to change…
Mine ended up looking like this…
WINDOW_MJH_EXAMPLE.gh (82.1 KB)
My outer frame is separate components but I left the actual windows as simple solids as I haven’t decided how I will manufacture those yet. It is easier to model simple solids than have each and every timber component modelled and related to each other so if you tweak one parameter, all related dimensions change.
I think the key to doing this sort of definition in GH is to have good terminology for all the parts of the model… for example, I have a window frame and then window frames within that outer frame. I kept getting frames confused when I tried to make changes.
Sometimes you can use an offset to put a pane within a frame, for example, but sometimes you might have a different offset in X than Z so it is better to move the reference plane.
Anyway, hope this helps rather than confuses further!