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 .