Is it cheaper to build an attached or detached garage? Follow In general, it is cheaper to build a detached garage than it is to attach a new garage to your existing building. Related articles Can my metal garage be attached to an existing structure? How much does a metal garage cost? Can I have a two-story barndominium? Will General Steel refer me to a local erector or contractor? Does an attached garage raise insurance? Comments 0 comments Please sign in to leave a comment.