You don't want pressure treated wood and it will have to be painted to last outdoors. Preferably use an exterior latex paint to keep fumes from the paint down or let it cure for a while before placing chickens around it. Insulation depends on your climate. Adequate ventilation is necessary to keep ammonia and humidity from building up inside so unless you are in an extreme environment that would make insulation somewhat pointless. People have different ideas of a coop. Will your chickens be confined to it all the time or use it for nesting and sleeping and have access to a run during the day? Adult full size chickens need about 1-2 ft. of roosting area. If they are confined to the coop for any length of time then at least 10 sq. ft. per chicken. The floor of mine is plywood with a white "roof in a can"(Commonly used on camping trailers and mobile homes) that applies like paint. Some use sand or pine shavings to make cleaning easier. I use PDZ stall freshener but have a very small coop with an attached run as I only have four myself and live in a warm climate. It absorbs the smell and is easy to clean.
