The cost of a porch could be anywhere from $5,000 for a simple structure or less to $75,000 or more for a sunroom or similar fully enclosed structure. The cost to build a 16' x 20' covered, enclosed porch is approximately $60 to $100 per square foot, or a total of around $16,000 to $32,000. Larger porches generally cost less per square foot while smaller porches tend to cost more per square foot. Pouring a concrete slab costs around $5 to $10 per square foot.