Don't be afraid to use cardboard :) This site links you to lots of ideas for kid play-friendly items made with cardboard.
Shield Craft to Go With Book, The Knight and the Dragon by Tomie dePaola
A Preschool Theme on Kings and Queens that Will Make Your Classroom Royal
Knight Shields Kids Craft //cute for Shield of Faith & Armor of God
DIY: Castle Story Box - The Imagination Tree, http://theimaginationtree.com/2011/05/diy-castle-story-box.html
Kids learn about castles, royalty, architecture, shape and line with this fun art activity inspired by children's books!
A cardboard castle by my favourite designer Ann Wood. Super fun to do with kids on a weekend.