wagon-headed

from The Century Dictionary.

• Having a round-arched or semicylindrical top or head, like the cover or tilt of a wagon when stretched over the bows; round-arched: as, a wagon-headed roof or vault.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Having a top, or head, shaped like the top of a covered wagon, or resembling in section or outline an inverted U, thus �.