You'd probably be best off making one from scratch out of a large styrofoam cooler. Don't ask me the size. I've tried not to think about it because everytime I see those giant green eggs I tell my husband I want one.
Now before you "want one" you have to think about fencing. I know it sounds crazy but before my husband would put up an inch of fencing on our property he asked us all the animals we could possibly want to put inside.
His theory was that he was only going to put up a fence one time. He was not going out to reinforce it because suddenly we wanted Llama, or Emu or Giraffe!
Surprisingly Emu and Ostrich take quite a bit of fencing. So before getting into these birds, I'd make sure you have the fencing to contain them.
A place to put an emu is not a deterrent for me. I remake fences yearly. I've been running our horse stable since my grandma passed away when I was in junior high. Taking down a mile of fence and moving it so we could plant a different section as hay and use an old section of hay field as pasture is just a standard spring event here and usually 90% my job. The other 10% being someone to run the tractor and lift the bucket up and down while I wrap the logging chain around tposts to pull them out. I'd have an emu fence up in a week. When I got a puppy I had 1000' of field fencing up for my dog yard behind the house by the end of the weekend. My back hurt for the next week.