I just started using our old polydome calf hutches for brooding chicks of different ages, I think we have 20 of those big plastic igloos sitting around rotting! For the longest time I was trying to convince DH to sell them before they all broke down. Now I use them all over the place.
It was really one of those Duh! why-didn't-I-think-of-that-one-earlier? moments when I first started using them for chicks. I cut a piece of 1"x2" welded wire just a little bigger than the opening, I bent the side so they would follow the curve of the hutch door then I used the pipes (the ones that would typically hold the manger in) to hold the wire on the front.
It's probably not the most predator proof solution but I haven't had any problems since I started using them earlier this year.
I'll try to get some pics tonight to post tomorrow. If you have any of these sitting around, they work great. If you're lucky enough to know a former dairy farmer who wants to get rid of some, or better yet, loan you some, go for it. The only problem (at least around my area) is that most people won't part with them for cheap. I've seen advertisements for used hutches anywhere between $150-200 a piece