Ours are on thick layer of shavings, I change them weekly, the brood lamp seems to keep shavings dry although they make a mess with crumbs and water.
Out brooder is a large plastic storage box with a mesh lid, I fixed the heat lamp height but connected it to a dimmer switch so I back off the switch slightly every couple of day. At thee weeks they go in the shed in a larger run made of planks, again on shavings with another heat dimmed lamp. 5- 6 weeks or so should be off heat completely.
Listen to them, they will tell you if you are hurrying the process. Our brooder is in the kitchen and the other night we couldn’t hear the TV for them squawking. It turns out I had unplugged the brooder by mistake while making some toast and they were cold. Plugged them back in and they were all happy, if a little indignant at my mistake.