I never did make one, tbh I ended up siding with the butterflies, I made an enclosure to let the caterpillars live in to give them more of a chance to get to that stage, I built it out of 3x2s and covered it in netting then placed a few nettles in. it turned out all right.
Now I have a new allotment I am going to make some space for it once again, it was great when you're letting them fly right from your hands. my kids loved it too.