You can make this cute barn using a cardboard box, scissors, and paint. The barn doors even open and close. If you want to put your toy animals in the barn afterwards, make sure you start out with a box that is the right size for your animals.
Mark the cardboard box so that it has the roof-line of a barn.
Cut the cardboard along your markings, making a barn shape.
For the roof, cut a rectangle of cardboard that is about an inch or two longer than the barn and wider than the two triangular tops of the barn.
Mark where the fold line will be and then carefully fold the rectangle in half. Place the roof on the barn to make sure that it fits.
Mark where you will want windows on your barn.
Paint the barn red.
When the red paint dries, paint the inside of the windows black. When that paint has dried, paint white trim around the windows and doors. Also paint a large white "X" on the barn doors.
Paint the roof white or light gray.
Place the roof on the barn.
You now have a fantastic barn with a removable roof.
A cardboard box (pick the size that will fit your plastic animals)