Michael Heilemann has an amazing piece on his website kitbashed.com on the history of the development and design of the Millennium Falcon. Its more than worth a look. Heilemann goes in depth in examining the evolution of the designs of model maker Colin Cantwell and concept artists Joe Johnston & Ralph McQuarrie.
Original Star Wars concept designer and director Joe Johnston posted his memories of the development of the ship on his Facebook page. Read it online here.