Start with the footprint
Measure the approximate length and width. Note the height from grade to the door, where stairs could land, and whether the deck must work around utilities, windows, or HVAC equipment.
Choose the major features
Decide whether you want railings, gates, skirting, a roof or cover, multiple stair locations, built-in seating, or a picture-frame border.
Think about daily use
The number of people, furniture layout, grill location, shade, privacy, and traffic flow can change the best layout.
Photograph the whole area
Include wide property views, the door or entry point, the ground below, access for materials, and closeups of any existing damage.