Cost to Build a Deck by Size Size Pressure-treated wood Average cost Composite decking Average cost 10x20 $1,300 $2,800 12x12 $936 $2,016 12x20 $1,560 $3,360 14x20 $1,820 $3,920 3 more rows Calculate the Cost to Build a Deck decks.com https://www.decks.com � calculators � cost-to-build-a-deck decks.com https://www.decks.com � calculators � cost-to-build-a-deck Cost to Build a Deck by Size Size Pressure-treated wood Average cost Composite decking Average cost 10x20 $1,300 $2,800 12x12 $936 $2,016 12x20 $1,560 $3,360 14x20 $1,820 $3,920 3 more rows