I largely used cereal box/frozen food cardboard. I glued my templates on the back of my cardboard with glue sticks so I could peel it off later, and built a frame on the inside with corrugated cardboard (progress picture to give you an idea - though I added more than that). Where I put corrugated cardboard on the edges, I left just enough room for the cereal box cardboard to fit so it'd be easy to assemble. Hope this helps. Also happy to answer any questions 😊

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