I've assembled a list of my favorite Roycroft copper reference materials:
"Roycroft Art Metal" by Kevin McConnell (has been printed in three editions)
"More Roycroft Art Metal" by Kevin McConnell
"Official Price Guide To Arts and Crafts" by Bruce Johnson (has been printed in two editions)
"Head, Heart and Hand - Elbert Hubbard and The Roycrofters" by Marie Via (This book is so well done, and includes so much interesting information, that I consider it to be a "must have")
"Roycroft Collectibles" by Charles Hamilton (has been printed in two editions)
"The Book of the Roycrofters" by House of Hubbard (a catalogue reprint)
"A Catalogue of the Roycrofters" by Stephan Grey (a catalogue reprint)
"Tookay" by The Roycroft Arts Museum (a 1912 Karl Kipp catalogue reprint)
"Karl Kipp and His Work at the Tookay Shop" by The Roycroft Arts Museum (a 1914 Kipp catalogue reprint)
"Arts and Crafts Metalwork and Silver" by Wissinger (Some really nice Roycroft pieces are shown in this little book, including a page full of rare Italian polychrome stuff, some German silver pieces, and some rare bookends. The photography is nice too)
Original Roycroft printed materials including sales catalogues, The Philistine magazine, and The Fra magazine are a useful source for indentifying Roycroft copper items, and they make for interesting reading.
Most Arts and Crafts auction catalogues such as "David Rago Auctions" and "Craftsman Auctions" include Roycroft items and are an excellent resource for current prices.