I am going to do the same thing. We have a detached barn that has a cement floor and it has been retrofitted for a two car garage. It is huge, two stories. We never put our cars in due to toys and stuff, but I bought my husband a 10 x 12 metal shed of his own, and now he has moved much of his lawn equipment etc. out there. So we have a corner free. It is very cold to the extreme here in NH, and I hope building my coop in my barn will help with warmth and overall cost of the coop. Sounds like it will. It will not be "pretty", but my 5 chickens will be happy, and with the run behind the barn facing south, it is the warmnest and least windy place on our property. I hope I am making a good decision.