My brooder is just a large dog crate from PetSmart with wood on the sides and a divider so we have two different "pens" for different breeds. Heat lamp in each. I'll try to get a picture later.
I built mine out of those storage cube panels that you put together with the plastic connectors. In addition to the plastic connectors, I zip tied everything too. I put cardboard in the bottom and up the sides and filled it with equine pine and shavings. It worked out great.
Because I have cats, I also enclosed the entire thing in that plastic fencing stuff to keep the fuzzy butts from becoming a midnight snack for one of the cats.