This past weekend I made a dropped ceiling for winter in my pole barn. This is the 8 X 12 area where the chickens roost at night and where I'll hang a light bulb all night when weather is below freezing.
I made it with 2 X 4 studs on end,dropping them down to about 7 feet. I bought sheets of 4 X 8 PVC corrugated panels, they are crystal clear and let the light from the clear roof panels shine in.
They are pretty thick so they will cut down on drafts and reduce the cubic air space that needs to be heated by bulb or chickens themselves.
Because they just lie on the studs, I can easily take them down in the warm weather, hose them off and store for next year.
Heritage Hens