This is a near-impossible question to answer. If your deck is in perfect condition, with no gaps, difficult railings, and so on, the cost per square foot can be as low as $1. However, if there are gaps, or if the railing difficultly enters the wall, the price can increase to $30. If you want to get detailed information on how much does it cost to build a roof over a deck, read our blog. Read more at: https://dailygram.com/index.php/blog/1064195/how-much-does-it-cost-to-build-a-roof-over-a-deck/