https://www.backyardchickens.com/forum/viewtopic.php?id=222358&p=2 is a stellar writeup of shipping!
http://www.hm-e.net/ designs, builds, & sells boxes.
I haven't yet shipped, but have received; four 1-2 year old birds.
I shopped around and ended up buying a 4-stall box from Horizon and...