I have a 10X10 run in shelter with good ventilation ( I am also putting in a fan), with barn doors to keep them in at night. It is on dirt, but I plan to put straw on the floor.
A. Sheep that are less than 1 year old are called "lambs." When born in the spring as are yours, they can also be called "spring lambs." Between one and 2 years of age, they are called "yearlings."
A dirt floor, covered in straw, makes an excellent place for sheep to bed down. The fact that you can close the sheep up at night will be VERY helpful if there are any predator problems in your area! It's also a useful option during rainy/snowy conditions, as well as at lambing time. If your fences are secure and the neighborhood relatively safe, older lambs and adults can certainly spend the night outdoors during good weather.