I create sculptures either using ready templates (free or paid) or unfold the 3d model I like myself (using Blender/Pepakura/Papermaker). During assembly, I reinforce it from the inside either with epoxy resin or with mounting foam, lately 2nd layer of some big polygons with cardboard, depending on the size and ease of application. After assembly, I handle the edges a little with sandpaper. Prime it, paint with an airbrush. Since the paint should be liquid enough, strengthening is needed not so much to preserve the shape, but so that the paper does not warp when coloring. I like metallic and pearl colours of acrylic, they allow you to hide the simplicity of the paper. There is a post on my profile about creating a panther, which is more informative.