Mine is the same size and I have 70 2 week olds in it. I usually do 100 at a time but ended up with with this odd batch.
I have a removable floor and a divider to make it 2 4x4 sections. I keep mine in the house the first few days and then move them to the brooder by day 5. I keep them in the 4x4 section till about 10 days then pull the divider. If the weather cooperates the I pull the floor out at 14 days and let them in the ground till 21 day, then they go to the tractors.
I have had times were the weather is so cold that I had to keep then in there w/ the floor till they are 21 days and it is an issue with the amount of poo the make. It will cap in areas around the feeder and waterer, this portion needs removed daily and fresh littler added.