That doesn't look like it's made from cardboard! We've had some great posts on cardboard furniture you can buy that doesn't LOOK like cardboard, but most DIY options resemble the brown recyclable stuff.
An Explorer's Home Office
estudio para uno q yo me se...
25 Awesome DIY Ideas For Bookshelves
étagère à livres
rangement pour livres en fleur, faite de boîtes (3 grandeurs) / Wow! A book shelf out of square boxes arranged in a circle. 3 different sizes --- such a fun idea!
I want this in my master bedroom for all my "casual" reading books (AKA paranormal romances.)