No one has replied yet, so I'll throw in a couple things...first of all, it will help if you post your location (doesn't have to be exact, just the general part of the country is ok) since building practices may vary in different parts of the country. Prices certainly will vary depending on where you live. Make sure you don't have any zoning issues with putting up a garage that big. Assuming you want to use roof trusses, 40' is pretty wide so they aren't going to be cheap. Also, combined with a 14' ceiling you will end up with a very tall structure that may visually overpower the house. What kind of building method are you thinking of - a pole barn, conventional stud construction, red iron, or something else? Here is a recent video about construction of a 40x72 gambrel roof barn in Minnesota where he itemizes costs. You can extrapolate his numbers to get an idea of what a 40x40 will cost.