I mean I say :

Wall: {

  Start = x,y
  End=x2,y2
  Width = 9in
  Height = 9ft

}

Shelf: {

  Ref=wall1, wall2

  Start = ....

  End = ...

  Distancefromground=4ft
  Height=3ft

  Width=4ft
}

I just checked openscad. Thank you! Very good ! What other script to render programs do you know of?

I don't I'm afraid. Good search terms might be 'parametric CAD' or 'constraint', which are inherent features of script-based programs (but not exclusive to them, e.g. Fusion360).

Thanks for the pointer! I've recently discovered another trick- typing "openscad vs" in search bar