I saw this little door house on Youtube and thought it would be such an easy way to make a green house or a little cabin. French doors could be used or sliding glass doors. The roof could use a recycled sliding glass door as well for a green house. (?) I have a number of old standard doors here too. The slant roof could also be used to catch rain water. If it were being used as a small cabin one or two walls could be solid and a small shower and bathroom with a composting toilet could be built outside the solid door section. Look below.