Who if my neghbor's tree falls on my roof who ins. pays

Acts of God are tricky, and if there insurance won't pay but yours does you can request them to go after his insurance for recompense. Some times they will do this anyway. Call your agent and see what their policy on this is. But this is the law in Texas:

Injuries caused by falling trees, usually as the result of a weather event such as high winds or snow, are often defended as acts of God. While trees are normally considered an asset, they can cause serious damage and are a serious responsibility. Tree owners are responsible for maintaining the condition of their trees. A tree that is unhealthy or improperly cared for can quickly become a hazard. An extreme weather event will cause the inevitable to happen, but the responsibility lies on the party who allowed the tree to fall into a dangerous state to begin with.
There you go. Susu