Here is an outside (in a shed) brooder box that DH designed and built. There are 2 of them back to back in this picture. It is 4 ft. x 2 ft., has a wire bottom with inserts I can put inside, a wood base for a 1 gallon water, and supports for a trough feeder so if I don't have the floor inserts in place, I can support these without the wire sagging.
There are vent doors at each end, 2 pieces of wood that slide in under the wire for draft control (which are height adjustable).
On a newer version, he added a glass window in the front so I could have "chick TV". The window can be replaced with wire for summer time.
There is a heat lamp mounted on top.
Half of the top opens up, and he made a wire insert to put over the opening for more ventilation in the summer also.
We only have 3 of these left. We sold the newest versions. We have been using them for almost 4 years now. They don't look this good anymore!! We can brood 50 chicks for 2-3 weeks in one, and then we have to move half of them. Right now I have 4 Bantam White Cochins in one that are about 3 1/2 months old. I just don't have anyplace to put them yet. They are happy as can be in there.
We have another style that he builds too, but I don't have any pictures of it. It will brood up to 350 chicks on the ground in an enclosed coop or shed
Jean