We have a big plastic storage box with a clip on lid and holes drilled in it for air for smaller hatches. Inside we have a Brinsea 20 electric hen thing which works really well and costs a lot less to run than a bulb, aside from the lack of fire risk. After a few days they go down the shed in a converted pallet box which came with a delivery of willow shoots. I lined the sides with some poly carbon clear sheets to let light in but keep vermin out then put a hinged lid on it and at one end a strip of wire mesh for air. Works pretty well but tough to clean out.
My next plan is to build a custom brooder with 2 sections and a sliding divider in between. In each side the floor will have a snug fitting plastic greenhouse tray in it. When it needs cleaning out, the chicks are sent to the other tray and the divider closed. Then the tray slides out for easy emptying.