Our Homemade Brooder:

Click any picture to get a bigger view

Started out with a frame built using 1X4's and 2X4s and one 1X4 in the middle. Scraps were used for almost everything. This one is 5' by 2'. I had a few 5' boards and the 1/4" hardware cloth typically comes in 2' widths.
I also considered what my ground cover was going to be. I'm using a 6'X6' shower curtain - $2 to protect the floor. That's why I went 5 feet.
   
Mark the slots for the corners and cut diagonally. Push the corner 2X4's up from underneath. Then fasten them with wood screws.  This will allow the walls to flush up against the inside edge of the 2X4 frame so the chicks won't poop on the 1 1/2" lip.  You'll see more below. Fasten the flooring to the corner post with staples.
   
 I attached a 1X6 to hold the lamp assemblies to one end of the brooder. It's flush with the outer edges of the corners.
   
Now the side rails.
   
 I'm sure I'm not using these correctly, but if you put them on straight up and down, they're less than 1/4" from the edge of one board and would probably split it.  So, I tipped them.
   
We used a Dremel to grind these down - more for us than the chicks. But you don't want anything sharp in there.
   
Mom on the Dremel - NOTICE Safety first.  You can see one of my pens behind her.  The birds are too young to put outside yet.  And if you look close, you'll see the shower curtain with cedar shavings on it below the pen.  Got to love a woman that can handle a tool!
   
Here you can see the end rails. Now with some old paneling scraps from a previous project I started building my coffin shaped brooder.
   
Here you can see where the wall is flush with the frame, preventing any pooping on the edge.  Only place is that center brace. But I figure they'll brush against it to keep it clean.
   
Same as above - outside view.
   
When I replace all the lights in the bedrooms in my home with ceiling fans, I hung onto the lamp assemblies that came off.  Here I drilled two 1/2" holes in that 1X6 and the outside panel for the wires to poke thru.
   
I tried to place the two lamp assemblies close enough to each other to work with the wires out side of the box.
   
Got them both on and the wires are outside ready for me to wire... Have to teach Mom that later.
   
Four bulb capability! In case one burns out, the chicks will be protected. They even have the globe holding nuts for a protective cover.
   
Here Mom is cutting the wire for a lamp protector to keep the chicks away from the actual bulbs.  We folded over the sides and fastened with plastic Zip ties.
   
Now to start framing the doors.  The brooder will have 2 doors.  The one above the lamps will be totally enclosed to hold the heat.  The other half will have 1" chicken wire for ventilation and viewing.
   
I added the duct tape to protect me from the sharp wire edges on the "open" door.  The chicken wire top allows for a place that isn't hot where the chicks can get away from the heat if it's too hot.
   
You can see I've already place the shelf liner mat down to help the chicks get their footing for the first few days.
   
Added a light dimmer to lower the intensity of the lamps weekly.  Also added some thin gauge wire to hold the door from falling all the way back.
   
 Be sure to read the schematic when you install these.  A ground wire and 2 black wires. One of the black wires goes to the black power cable wire and the other black wire goes to the black wires from the lamp sockets (load)
   
These are the 100 watt bulbs painted red with aquarium glass paint. The camera really shows a lot of white, but there isn't to my old eyes!
   
Here's my $7 WalMart thermometer.  I just turned the lights on for these pictures which is why its reading 67 degrees.  I placed the probe at the height of the chicks' bodies and about 3 or 4 inches in front of the lamps.  I'm expecting to get some false readings here because its attached to and outside wall (cooler).  I may end up poking a 1/2" hole in the top and dangling it down. That might give the chicks something to play with... a Thermometer punching bag.
   
 Here it is with the $2 shower curtain.  I plan on adding cedar shavings under the brooder to help the odor.
   
 Another view.  Good luck with yours!