Use of a propane grill on a terrace, balcony or roof is not only dangerous, but illegal. nachi.org has an article specifically on barbeque safety, as does mysafela.org. wiki.injuryboard.com has information on propane gas explosions and barbeque grill injuries, and it is reported that almost two thousand gas grills cause fires, which injure about 300 people per year. I personally have no experience with propane barbequers, though I would keep my small children at a safe distance from them.