I decided to put wire on the sides so that I could see in and the chicks could see out. I'm using a 250 watt heat lamp inside and another one up higher, just to keep the cooler end from getting TOO cool, but I'm probably going to take away the 2nd light tomorrow since our weather is warming up. I keep a thermometer inside to tell me the temperature, but how I really tell whether the temp is about right, I watch the chicks. As long as they aren't huddling tight under the light or piling up as far away from the light as they can get, moving about the brooder and making small happy peeps instead of loud distressed chirps, then the temperature is right.
I had most of the wood left over from a simpler brooder I made a few years ago. The big expense was the heavy-duty wheels, which were close to $100. I'm sure they are beyond what they need to be, but I wanted to be able to roll it over bumpy ground outside. I have an idea now that I want to try, for mounting a water jug on the outside, feeding through a tube into a small water dish inside, to give more floor space. I haven't figured out just how to do that yet, and it may wait for the next batch of babies next year. It's fun to figure out better ways to raise the babies every time around!
Oh, and I meant to say, a 100-watt bulb may be plenty for your brooder--it just depends on how warm your room is. My brooder is out in the unheated garage, so it gets cold at night.