I built this same shed on a wooden foundation.The inside of the shed.
https://images.thdstatic.com/catalog/pdfImages/18/1802dd4d-dbc6-447a-a6bc-35764f64f785.pdf
I'm kinda worried that once I start removing metal sheeting on the sides it won't be structurally stable.
4x4" posts down into the ground(frost heave here), 2x8" joists and 3/4" floor sheathing....all pressure treated. I also added a large double door with a ramp to drive a snowmobile inside. The door was framed in wood and sheathed in the metal siding cut out for the door.