Reply by RonInOhio

The common number I see floating around is around $25 a sq. ft. roughly. For a 12×18 building that comes out to $5400. Ballpark number. Probably on the low end of the spectrum.

I see some other numbers in here that are ~ 25-30 % higher or more, but you are probably going to be shopping around for the builders and you are likely to get estimates that will fluctuate from high to low by that amount.

Other factors such as where you live and the number of contractors in your area would also factor in. As well as what type of foundation, insulated or not, electrical,cost of permits, etc.