This is the one book that I would recomend. The detail in the book is great, and it is small and light, always a must on long distance walks like the West Highland Way.
West Highland Way: Glasgow to Fort William (British Walking Guide S.) (Paperback)
by Charlie Loram
Includes ten town plans and forty-eight scale walking maps at just under 1:20,000 – showing route times, places to stay, points of interest and more. This book also contains itineraries for walkers; and practical information for various budgets.