Average Home Building Costs Per Sq Ft: Shell Option. The average home building cost per sq ft for a home is far more uniform than the finished cost per square foot. A shell does not include the foundation, landscaping, fixtures, cabinetry finishes or appliances. Sometimes it does not even include drywall. It usually doesn’t include the plumbing or electrical wiring either, though sometimes rough plumbing and wiring are included. The average home building cost per sq ft for a shell is about $25 per square foot with a range of about $22 to $30 per square foot.