I'd say raise it, and insulate the hell out of it... our coop is the old one that was left on the property, it's attached to the barn, but on the outside and when I get my hands on it!... it's getting some SOOOPPPPERR DOOPER insulation, because this winter was insanely cold, and lasted insanely long. I'm putting in not only GOOD insulation (it's in my garage LOL, and seriously...before we put it in it was below 0 all the time, and now it's like 10 degrees in there during the winter) which is fire rated, in the ceiling, doors, and floor... I think the floor is concrete, but we'll be raising it to put insulation in, so it'll be a concrete floor, and then likely a wood raised part with some stickon tiles on it, for easy cleaning. Anyway, firerated insulation floors, walls, and ceiling. We have to do the firerated stuff, not only for our own comfort, but for our insurance cause we're more than 5km from the nearest firehall.