Horizontal lines on ceiling, roof leaking
Ecnerwal is spot on.
While you figure out how to fix this poke a few holes through the ceiling and place a bucket underneath so the water can get through. It may seem worse initially but remember the water has to go somewhere. If it isn't coming through the ceiling then it's soaking into the drywall and insulation and the extra weight might bring the entire ceiling down to say nothing of damaging even more.
Jonathan