ridgepole, ridge
棟 centers on the main horizontal beam at the peak of a roof: the ridgepole. By extension it can refer to the ridge of a roof itself.
棟 combines 木 (tree/wood) with 東, which likely contributes the sound and may relate to the idea of something central or elevated, fitting the ridgepole as the central wooden beam of a roof.
The left side is wood 木, and the right side 東 looks like a sun rising behind a tree, suggesting the highest point. Picture the wooden ridgepole at the very top of a roof, like the peak of a sunrise.
For トウ, imagine a tall ridgepole on a traditional Japanese roof, and think of a towering temple: tower -> トウ, with the ridgepole at its peak.
ridge (of roof)
(hospital) ward
central figure; pillar (e.g. of the nation); mainstay; chief support; leader
separate building; outbuilding; outhouse
raising the ridgepole
one house; the same house
wholesale lease (on a building)
renting a whole house; cottage rental
general ward (of a hospital)
ridgepole-raising ceremony
ridgepole-raising ceremony
suffix for building numbers
top ridge of a roof; main ridge of a roof
hipped roof; hip roof; hipped roof construction; hip roof construction
hipped roof; hip roof
hip roof; hipped roof; building with a hip roof
dormitory building; dormitory hall
large building; building with a long roof
ridgepole-raising; setting up of the framework of a house
framework raising ceremony