In 2007 The Believer ran what I think is the definitive account of the Codex Seraphinianus: http://www.believermag.com/issues/200705/?read=article_taylo...
The Codex was likely inspired by the Borges story "Tlön, Uqbar, Orbis Tertius" which involves encyclopedia articles about an imagined world: http://art.yale.edu/file_columns/0000/0066/borges.pdf