Start by placing the moss in the lid covering it completely.
Next cut the doors and windows in the tube and start covering it with bark - if you are lucky to find super thin bark as we did you can make the doors and windows in the end. Regular white glue did an outstanding job.
Once that is done make a roof - we did it out of cereal box. We wanted to cover it with twigs but they didn't twigs so we decided to make a moss roof which turned out great (probably even better than the twig one would).