Having a shape broad as compared with the height, and bounded by rectilinear rather than curved lines: as, a square-built man or ship.
The Century Dictionary (Public Domain)
Use "square-built" in a sentence
"The early morning sun slanting in showed a cool, square-built room with a flagged stone floor, a raftered ceiling hung with bunches of drying herbs, and a heavy wooden table, the surface scarred and worn smooth and dark with age."
"The space was windowless, square-built, and with only one door, smelling of unseasoned timber and straw from the thatched roof."
"It was a square-built room, very plain, with lime-washed plaster walls and a rush-strewn floor."