We built a box but it's barely too big for our mini guernseys, so it'll be even bigger on our nigies. We put towels on the bottom to make them taller but they could just squeeze their heads through the neck hole. We ended up keeping them in the box but I had my hand on top of their neck, forcing then to keep their heads out. I've read where people would put towels in the neck hole to make it smaller. I'm not really sure if this makes sense, but I hope it helps if you can't get/make a smaller box.