Hi Lila. Here are a few projects for trellis builds. The first one uses pallets. Hope that helps! https://www.hometalk.com/search/posts?filter=diy%20trellis%20pallets
I would use lattice that comes in vinyl and needs no upkeep, and cut it to size and stabilize it with pallet wood on the edges.
This is how we made our Rose trellis. We used lattice, but you could easily put in pallets there: https://chemistrycachet.com/diy-rose-trellis/