Your question is a bit too open ended. Are you interested in building airframes, autopilots, or what. You will not find a single book which has much value in covering all UAV design topics.
There are a wide selection of well known texts dealing with beginning airframe design. It has been a pretty standard course in the undergraduate aerospace engineering curriculum at many universities for many years. You could start here - http://www.aircraftdesign.com/books.html. Raymer's text "Aircraft Design: A Conceptual Approach" is on the 5th edition and is a classic in in the field.
On the autopilot side there are few books which give a complete concise treatment to UAV autopilot design. As a starting point I'd recommend Small Unmanned Aircraft: Theory and Practice" by Beard and McLain. I have also found "Autonomous Flying Robots: Unmanned Aerial Vehicles and Micro Aerial Vehicles" by Kenzo Nonami, Farid Kendoul, Satoshi Suzuki and Wei Wang to be pretty good.
Many thanx Dough . Yes I should have been more precise , actually am interested in books related to the development of avionics for UAVs.