The top looks real good, but if that is plywood on the floor, i doubt that would last very long. Maybe a concrete block foundation around the perimeter and then about four inches of clean gravel. If you do not want to walk on gravel, cover the gravel with weed barrier and the water would still drain nicely.
The base looks like it was reused from a shipping container and a double pallet.
I've been dreaming of greenhouses for a few years now. Kind of convinced I want to build a geodesic dome greenhouse with a steel skeleton / frame. Covering the dome becomes the hard part. The other one that has caught my eye is a Walipini or other mostly below grade greenhouse.