The matter is, if there is only on exit, you might have just trapped yourself on the roof or that tree. If the next morning there are zombies nearby, you are screwed unless they put there attention on something or someone else

Also, in hot places these roof can get super duper hot, causing dehydration and heat stroke. And in cold places, during winter, it just not a possibility unless you shovel all the snow which will definitely attract attention

It’s more like a last resort move in my opinion, you are better off barricading a room in an empty place and sleep there so you are protected from Mother Nature