Wiktionary
barrel roof
n. (context architecture English) A roof having a semicircular cross section; used to span large distances in railway stations etc
Wikipedia
Barrel roof
A barrel roof is a curved roof that, especially from below, is curved like a cut-away barrel. They have some advantages over dome roofs, especially being able to cover rectangular buildings., due to their uniform cross-section.
Barrel vaults are a particular form of barrel roof.
Barrel roof.svg Barrel roof 02.svg
Usage examples of "barrel roof".
Above the windows and below the slightly jutting barrel roof Tonopah and Tidewater R.