so a while back I was commissioned for Aqua's "Stormfall" keyblade (kingdom hearts: birth by sleep) and I decided to document the process. this is usually how I go about making props, there's millions of methods and materials you could use, but I thought I'd contribute my two cents to the wonderful world of cosplay.
Your method seems a LOT more mathematical than mine. Granted I just skimmed the pictures but still. lol
Instead of measuring out everything, I just freehanded the overall shape on cardboard and cut it out. For depth and all that I just used insulation foam and carved it out. Definitely a long-ish process.