EVA/craft foam shaped with a heat gun, hot glue for assembly, sealed with elmer's white multi-purpose glue mixed with some water, and painted with acrylics. I eyeballed everything from in-game and a couple screenshots for reference.
it took me about two and a half months to build mine, but that's just because I used foam, and the sealing process takes a long time. If you build the piece first, then encase it in Worbla or Wonderflex, then you won't have to seal it. But I was on a low budget lol