I built a permanent three level brooder against a wall of my coop years ago and have been very happy with it. It is roughly 2ft deep, 8ft long, and 5 1/2ft tall. The bottom of the three levels uses the cement floor of the coop as its base. Each level has a removable center divider that allows it to become six seperate 2' by 4' compartments. Each of these compartments has a light with a metal reflecter suspended from a chain that will allow a standard 100 watt bulb to provide heat enough for day old chicks in cool sping weather, there is a hook that allows you to shorten the chain, raising the light as the chicks grow. The front of each section are double doors that latch in the center. I start chicks in the top section, moving them down as age and new hatches dictate. Evetually they get to the bottom level, when they are fairly feathered out I open the doors , allowing them the run of that section of the coop, but can still get under a light for cool nights. My coop is 12' by 32' that can be divided into three sections for breeding pens. By the time my oldest chicks are old enough to get out of the brooder, I am about done keeping eggs, allowing me to give that pen to the chicks.
A few years back I started vaccinateing for Marek's, which requires newly hatched and vaccinated chicks to be kept away from the old birds for the first two weeks. I built a smaller free standing version that I keep in the basement, untill they can go out to the coop.
Sorry, don't have photos (would have to delete shots that I have in other threads to make room)