I looked at a home for sale yesterday. The door to the deck off the kitchen was marked with a “Do Not Enter” sign, and “DANGER” was written large on that sign.
The deck and under it looked like this. Can you see why this deck is unsafe?
Keep in mind dozens of people are killed in the US each and hundreds injured year by unsafe decks!
In general because it is a structural renovation, decks are not a homeowner DIY project and they do require permits and inspections.