Finally finished the floor for that aluminum shed frame

I did almost the exact same thing with an old Arrow shed I picked up for fifty bucks. I used 2x4s for the joists but I acutally set them on top of 4x4 pressure-treated skids. Getting that extra four inches of air underneath relly helps with the humidity. My first attempt without the skids ended up smelling like a damp basement after just one summer becuase the plywood soaked up moisture from the ground trough the gravel. One thing I’d suggest checking is the seal at the bottom of the aluminum walls. I used some silicone caulk along the inside edge where the metal meets the plywood. Before I did that, rain woud hit the side of the shed and run right under the wall, soaking my bags of potting soil. If you find the plywood getting soft near the edges, a bit of flashing or even just heavy-duty weatherstripping can save those 2x4s from rotting out prematurely.

I went a diffrent route when I set up my 10x8 YardMaster. Instead of building a wood subfloor, I dug out about four inches of sod and laid down a leveling layer of sand followed by 12-inch concrete pavers from the local hardware store. I was worried about my heavy Troy-Bilt riding mower eventually bowing the plywood or the floor joists rotting out since my backyard stays pretty swampy during the spring thaw. To keep the aluminum frame from shifting, I drilled trough the bottom rail directly into the pavers using a hammer drill and some 1/4-inch Tapcon screws. It took a bit more elbow grease than just driving deck screws into wood, but I don't have to worry about the floor ever soft-rotting or attracting termites. I just threw a heavy rubber mat from Tractor Supply inside to catch oil drips and keep the mower from sliding around on the stone surface.

Since you're putting a lawnmower in there, that plywood is going to get beat up by oil drips and gas spills pretty fast. I’d highly reccomend rolling out a G-Floor Universal Floor Mat over the plywood. It’s super tough and will keep any fluids from soaking into the wood and causing it to rot or stink. I used it on my last shed build and it makes cleanup way easier—you just sweep the grass clippings right out the door.

Quick update—thanks for the advice! I decided to stick with the wood frame since it's alredy level, but that tip about the G-Floor mat was a lifesaver. I grabbed a heavy rubber mat to keep the gas and oil from soaking into the plywood. It feels solid now and I’m glad I didn't have to redo the whole base with pavers. Cheers!