I would think that pallets would be just the ticket if they are un treated. I don't know off hand how thick the pallet wood is, but I am thinking it's probably thick enough to nail or screw together! @ravenruis in their comment above mentioned they are thinking about making boxes with pallets too... maybe you could team up on a design :)
Thanks for the compliments on the porch.. I can't take credit as it's a rental house but I am enjoying the wrap around porch.. it's quite nice for hanging out, storage, workspace, etc.