-더래 relays what somebody else reported witnessing: 뒹굴거리다 밖을 보니까 해가 떠있더래 'they said they looked outside and the sun was already up.' Two layers stack up — the -더- says the original speaker saw it themselves, and the -래 says the current speaker only heard about it. These lines are storytelling among friends; adding 요 (-더래요) makes it polite.