If you're worried about warmth in the winter, you can put a "hover hood" over the roosts in the winter. I just made a steep a frame out of flashing metal and furring strips that I hang on chains about 2 feet over the roosts. It's just a bit wider than the roosts and steep enough to prevent roosting on top, and it seems to work well, as my birds don't huddle quite as tightly or ruffle up quite as much as they did before I installed it. The great thing about it is it still allows for plenty of ventilation while trapping a bit more heat at roost level. I have considered gluing some styro insulation and luaun on top of mine to improve it somewhat, and possibly rigging a couple of 100 watt bulbs in coffee cans under it for the few really severe cold snaps we usually get here in NE Texas. It's probably overkill but I'll sleep better for it, so it's worth it.