Repton presented his advice to his clients in the form of Red Books, a term referring to their characteristic red morocco bindings. A typical Red Book would begin with a ground plan summarizing his proposals. An introductory epistle would address the client in suitably deferential terms and recapitulate the terms of the commission. Then would follow a description of the client's property, commending its scenic attractions, noting its defects, and suggesting how improvements could be made. The approach to the house, the park, the pleasure ground, and other important features would be discussed in separate sections accompanied by watercolor illustrations. Some of the watercolors would be equipped with overlays allowing an easy back-and-forth comparison of the property in its present state with Repton's recommendations for its future embellishment. In a mellifluous conclusion, Repton would urge the client to follow his advice, which, he implied, would not only enhance the enjoyment of the estate but also display it in a manner befitting the owner's good taste, family pride, and social status.
Repton regarded his Red Books as working plans, advertisements, souvenirs, and a convenient source of documentation he could use in his publications. His Red Book of the Welbeck estate provided the "groundwork" of his Sketches and Hints on Landscape Gardening, which contains extracts from fifty-six other Red Books duly cited at the front of the volume. He claimed to have made more than four hundred of them by the time he had reached the end of his career. More than a hundred survive, an indication of their importance to his clients and their value to scholars and collectors.