cost of building a garage addition
1 According to author Stu Silverman the average cost of adding a garage begins at roughly $7,500, and for a two-car garage the average costs will go much higher. 2  This sort of structure will average at $27,040. 3  The resale value of this update would hold at $21,635, or a nearly 81% return on investment.dding a garage to a home can require an extensive amount of work, and for this project we will assess the cost of building an attached garage of 676 square feet (26'x26') to a pre-existing home (this is going to easily accommodate two vehicles, provide storage and even have room for a small work area).