Not too sure. I see it being made by just pushing the ends into the ground, so it would end up looking like a very small hooped tent! Without the fly sheet!
I suppose you would need to get a few billy cans on top, so maybe a couple of feet long by a foot wide, and maybe 8 to 12 inches high? Total guesswork of course, maybe some of the archealogical sorts could give us a more definitive answer. Saying that, I think the experimenting is half of the fun!
I'm thinking we may be told to build it on top of stone slabs or even one of the existing fire altars rather than directly onto the ground? I will look at collecting some material tonight.