Here is how I made my brooder:
#1: I built the frame for it. The outside dimensions for the wooden frame are: 4 feet wide, 5 feet long, 4 feet tall. On the front, (One of the 4 foot wide sides) I put a board lengthwise about a foot off the floor. I put plywood on it, except for the top half of the front. (Picture 1)
#2: Next, I cut a piece of plywood for the front. I screwed hinges onto it and put a latch on the top.
#3: I then put the wheels on the bottom, and they are lockable, so your brooder doesn't run away.
The 2x4 across the top is to hang a heat lamp and/or a feeder from. If you have any questions, please comment.