I notice that the link I gave you was for a lightweight, aluminized bubblewqrap hover for broiler chicks... did you read on to where he recommends a plywood one for non broiler breeds, so they can roost on top? (That is what I meant to link to, sorry!)
Basically you make same thing but outta 1/2" plywood (sides are 12" hi), and with top of box recessed 4" below tops of sides - can then pile shavings on for xtra insulation, plus gives birds somewhere to practice hopping onto roost type thing when theyre a little older. And he uses porcelain light sockets, attatched 4" above bottoms of sides (that is, attached on the inside sides of box) using plastic electrical boxes on outside rather than just screwing into flimsy plywood. In book, he discusses use with draft guards for drafty environments as well.
Hope this helps,
Pat