This is a look at my converted baby barn into a pigeon loft. Hope you can use it for a template if you decide to build. It is not insulated and my pigeons are subject to -40º. I feed extra whole corn in a separate feeder. No problems.
One suggestion when building a loft it is a good idea not to make it higher than you can reach comfortably. Installing a drop ceiling of chicken wire is a cost effective way of accomplishing that.