You want to build one? Here's what I suggest.
2x4 frame-you choose the size according to how many chicks you want to raise. Put it on legs so that it is up off the floor at a comforable working height. That saves a lot of back aches.
Hailscreen floor-no larger than 1/2" holes.
Plywood of up to 1/2" thickness. A lot of times this can be salvaged from other projects. Use this to enclose the sides.
1" material to build the frame for the lid. Use hailscreen or similar to cover the lid.
Heatlamps as necessary for your climate. I put my 2x4 legs extended up high enough that I can put another board across between them to hook the heatlight on so I can raise or lower it as necessary.
Take a look at John Blehm's website.
www.chickhatchery.com I belive is the website. Somewhere on there he has pics of his brooders.
After saying all of this, my last brooder was a big cardboard box.... until they got big enough to fly out of that, then they were moved to an oblong stock tank out in the shop with a welded wire lid to keep the shop cats from having a chicken dinner.
We built several brooders like this a few years back. Unfortunately they were left behind when we moved. Much of how my projects turn out depends on what materials I can salvage for them. It's not too tough. Have fun with your project.