I made a 3X7 brooder and it should hold 50 or so for a while and I am building a 4x6 Brooder out of scraps left over in my barn and its about 3/4 the way done. This one should hold 50-65 or so. I'm glad I spread out my orders a few weeks apart! Hopefully by 3 weeks I have them off heat!
Big box from grocery store. The kind they use for watermelons, etc. You know, those huger suckers.
A sawhorse
Brooder lamps
Use a couple of nails in the sawhorse to help secure the lamps. Place them apart a bit.
I use the top of those boxes as a floor. If they don't have the top I tape flattened baxes together and lay them on the grount. Then take the big box and tape the bottom to the flooring.
I like this way, because after I'm done I can toss it.
I put my 30 chicks in their coop when they were a week old. Their going on three weeks old now. The coop is 330 sq ft. They look like ants running around in this big coop but they love it.
Easiest to partition off part of the barn or garage. Yes, they'll need 100 sq ft, I agree. Use the corner of the barn or garage and you'll only need to "build" two sides. Those sides will need to be every bit of 3' high as the 5 week old chicks love to see how high they can jump/fly and perch.