Why did Jesus kill a friend on the roof of a building?

That is one of several stories from ancient writings that were not accepted into the biblical canon. There are several such non-canonical gospels. If memory serves, Jesus was angry or jealous with his playmate and tossed him off the roof. He then thought better of the whole thing and brought the child back to life. Another story relates how Jesus made some birds from mud or clay, and then breathed life into them and let them fly away. I think these stories are from the writing called the Gospel of Thomas.