Try describing this in C#

Models.fs

namespace Arealities.Models

type Size = Size of decimal * decimal * decimal
type Position = Position of decimal * decimal * decimal
type Rotation = Rotation of decimal * decimal * decimal
type Direction = Direction of decimal * decimal * decimal

type LightIntensity = float
type Material = Ground | Floor | ShinyStuff | Wall
type Geometry = CubeGeometry of Size
type Color = Color of float * float * float
type Mesh = {
        geometry : Geometry;
        material : Material;  
        position : Position;  
        rotation : Rotation; 
        castsShadows: bool; 
        receivesShadow: bool
    }

type Object3D = 
    | Object3D of Mesh list
    | Mesh

type Light = 
    | AmbientLight of Color
    | DirectionalLight of Color * LightIntensity * Direction

type Camera = Camera of Position * Direction

type SceneObject = 
    | Light
    | Object3D
    | Camera
          
type Scene = Scene of SceneObject list

maybe you can use a record for Mesh instead of a discriminated union ?

I'll take a look at records; thanks for the tip!

adjusted!