It would help answer the OP's question if he would give us a little
more background. How big is the hutch? How tall? If it is small
enough to glue the shingles down without having to crawl around, it
would probably be fine to glue them with roofing cement. On something
that small, I don't think felt is necessary. I don't think they'd
take much abuse, however, like walking on them, large amounts of snow
and ice, etc. Perhaps as someone suggested a urethane caulk would be
better. You might want to experiment. Having said that, I still think
you'd be better off with some type of nail, though itdepends on the
project. What are the consequences if a shingle falls off? If it's
no big deal, then go for it. If the owner is going to sue your ass
for emotional damages because their bunnies got wet, then better nail
down with 5 nails per, two layers of ice and water, tar every shingle,
etc .