by Jay Behm-A very basic way to estimate the cost of building a detached garage is to simply apply a typical average per square foot construction of $30 to $40.That is for an average cost basis for having a contractor / builder build a basic one story garage for you on your property.f you are in an area with higher-than-average cost of living you can use $50 to $55. If there are complications or you prefer top quality materials and components the price can go up.So, generally speaking, a 24 ft.sq., two car, basic garage will cost in the range of $17,000 to $23,000.