Measure the assembled framework floor area of the shed floor kit with a tape measure. Use the outside edges of the framework to make your measurements so that the floor, when installed, covers the frame flush with its edges.
Transfer the measurements to a 3/4-inch plywood sheet using a pencil and a straightedge to draw cutting lines onto the plywood. A single sheet is sufficient for the smallest kits. For larger kits the kit instructions have measurements and layout instructions for each plywood sheet to cover the frame in a way that allows you to screw the plywood in place along the wood sheet’s edges into the framework metal. Follow the manufacturer’s instructions on sizing if your frame is large enough to require more than a single sheet by marking the sheets with cutting lines according to their measurement suggestions.
Cut the sheet along the marked lines using a circular saw.
Lay the plywood over the framework. Follow the manufacturer's recommended layout guidelines to place multiple sheets. The edges of the outside sheets should be flush with the edges of the framework, with interior sheet edges adjacent to one another closely butted together.
Drill pilot holes into the sheets at the edges through the sheets and into the frame beneath, spaced every 12 inches. Attach a screwdriver bit to the drill and then use the pilot holes to drill one-inch drywall screws through the plywood and into the frame to secure the plywood floor into place.