If you are planning on studying Charleston architecture, you had better clear some shelf space. There are a number of good books, as many bad ones, and a few essentials. Indeed, you may find, in time, perusing your shelf is a study all its own of Charleston, the modern tourist city. Following is a short, starter list to aid you on your journey.
If you are merely visiting Charleston and have to have only one book, and a light one at that, I would suggest either Charleston: A Historic Walking Tour or Historic Homes Charleston South Carolina: A Pictorial Guidebook. Mary Preston Foster’s Charleston: A Historic Walking Tour (Arcadia Publishing, 2005, ISBN: 978-0-7385-1779-7) has the advantage of being compact, newer, and organized along three walking tours. Walking is the best way to see Charleston. But with its black and white photography, Charleston: A Historic Walking Tour is not as pleasing to the eye in an airplane seat, or back home in a recliner. For this you might consider Historic Homes Charleston South Carolina: A Pictorial Guidebook by Bryan Riggs (Charleston Postcard Company, 1993, ISBN: 978-1-56944-007-0), which is in color. While not a walking tour, this book is organized by street, which works out reasonably well when traversing the streets of Charleston.
While these books are satisfactory for a casual visit, if you are serious about your studies you will want to have the more comprehensive The Buildings of Charleston: A Guide to the City’s Architecture by Jonathan H. Poston (University of South Carolina Press, 1997, ISBN: 1-57003-202-5). This definitive work, compiled for the Historic Charleston Foundation, contains a number of essays on various aspects of Charleston architecture, from its history to its wonderful wrought iron gates. It also contains street-by-street, house-by-house thumbnail photographs and descriptions.
Reading these descriptions is enhanced by some knowledge of the architects and the world that produced these marvelous buildings, for which I suggest Architects of Charleston, by Beatrice St. Julien Ravenel (University of South Carolina Press, 1992, ISBN: 0-872-828-X). First published in 1945 by the Carolina Art Association as part of the awakening to the rich cultural heritage possessed by Charleston, Architects of Charleston explores not only the famous–Robert Mills, William Drayton, Gabriel Manigault–but many, many lesser known architects of Charleston as well. The book is graced by photographs taken by the prolific Southern photographer and engineer, Carl Julien, who appears in several other books on architecture, including Beneath So Kind a Sky: The Scenic and Architectural Beauty of South Carolina.
There are many, many other books on Charleston, but these are a good start.