My sheeting is on the outside of the slab, so there's lots of gaps for grass to grow through, wind to blow in and 'things' to come in through.
Before I bought this place and was looking at building on an empty block I went to a local shed supplier. I was impressed at his solution which is to form an inset on the outer face of the slab when it's poured. Say it's a 100mm slab then it would have been about 50mm down the side from the top and about 50mm wide cut into the slab.
Then the sheets are outside but sitting on that ledge so nothing can get in but it's still off the ground.
