I had no clue this website even existed, and while I have a feeling that I say that quite often I am still constantly surprised by the creativity and sharing of such that goes on online.
Instructables is a place where you can explore, document and share your creations. There is a whole section on outdoor projects. I found this one above on Treehugger and love it. Naturally cool cob playhouse cost $30...... and has a grass roof. What's not to love.