Ginny and John Stimpson lucked out when they found an early 1900s home on the bay in Fairhope, Alabama. "It's just like living on a lake, except we're about a 45-minute boat ride from the ocean," says Ginny, who planned and oversaw the house's renovation herself. She kept the updates authentic and didn't add on any rooms. While the result is a breezy waterside cottage that's the ideal size (2,300 square feet) for Ginny, John, and their three sons, it can fall short on space when company arrives. Youngsters can bunk on the main house's sleeping porch, but she believes the adults deserve creature comforts (like air-conditioning and a private bath), so she turned to the property's sturdy stand-alone garage. Careful to stick within the confines of the existing structure, Ginny came up with a smart plan: 70% of the garage's 480 square feet would be used as a guesthouse; the remaining 30% would be dedicated to storage. Read on to see how she turned the building around.