I love open air barns, mostly cause it is hot here in the summer. 16x16ft stalls minimum. I perfer 20-25 gallon water buckets. That way I know how much they are drinking. I perfer sand stalls less maintenance, good drainage, and great for horses who have feet problems. Water hot and cold, electric, nice take area with a little fridge (for medications or drinks or carrots and apples) .

It's fun building a barn.