The course will be based off of the slides that they send you. Reference books should be based on the test specifications. If a code has been updated, you don't want to lose easy points because you went by the new code vs the old code in the test specifications. Other reccomended books may be a good reference guide for extra reading or additional details. For example, Caltrans (California DOT) has a lot of construction manuals online that cover test subjects that can be used as additional study resources to go more in depth in certain areas. Part of the Construction Depth course, there were a few charts uploaded from the different guides ( due to copyright laws they are restricted on what the can copy and distribute), however as many people can tell you all the information in the guide is free game in terms of possible test questions.