The following are links to posts on his blog which show his illustration process on two projects for Barnes & Nobleā¦
http://gregnewbold.blogspot.com/2015/05/barnes-noble-table-topper.html
I chose the first post because it s how a nice collection of rough concept sketches that he created poster project:
This second post shows another project for the bookstore chain, but this time it is a mural for the Tribeca Store in New York City.
http://gregnewbold.blogspot.com/2015/12/barnes-noble-tribeca-store-mural.html

While this post is lacking initial rough concept sketches like the first project, it does show the in depth interaction an illustrator typically has with a client start to finish on an big illustration project:
You can see more of Greg's illustration blog postings at http://gregnewbold.blogspot.com.