The technique for this type of construction is to start by fixing the studs on the wall. Then, build each level of the metallic structure.
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Each level is covered with panels. In this example the material used for the horizontal panels is wood, to support the weight of books.  Wood is also used for the second and third level vertical panels, which is needed for the adjustable shelves. Every other panel material is plasterboard.

Plug the holes with filler, sand, then apply a finishing coat.

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Paint and install adjustable shelves.

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Et voilà !