Love that. I have pallet shelves in my greenhouse too but I just stacked some cement blocks and layed whole pallets on them. That's much prettier. I have some hog panel arches too but I'm short so they work for me straight on the ground. Poor hubby has to duck...might try doing that so he can use the space better too.I'll have to check into that. I have a neighbor that has a canopy like that for his pickup. But he takes down the roof in the winter. I don't imagine it is strong enough for our snow loads here in northern Minnesota. His canopy roof is too flat. But maybe there are other options with roofs that would shed snow.
As for the pallets on the bottom, I have been looking at a number of greenhouse builds where they use pallets for the bottom base wall and then use hog/cattle panels for the arch above.
With pallet wood shelves inside something like this...
I like a number of pallet greenhouse ideas in the following 30 mins YouTube video. Maybe too long for many, but that's the kind of programs I watch these days.