Working with Textures, Models, and 2D - Mastering Unity Scripting - page 290

To start, create a new empty object at the scene origin (named SkyBoxCamera ) and
add a first-person controller object as a child. Then, create six Quad objects from
the main menu (by navigating to GameObject | 3D Object | Quad ), aligning each
object to the corners of the other, with the vertex snapping to form an inverted cube,
that is, a cube whose faces are turned inwards, as shown in the following screenshot.
This represents the mesh for the manual Skybox.
Create a manual Skybox from six Quad objects
Scale the Quads if required and make sure that they contain and
enclose the first-person controller, which should be at the center
of the Skybox.