Truss and raised-beam frame
Two ways to hold up a pitched roof: the European truss, a rigid triangle whose tie beam stops the rafters spreading, and the Chinese frame of stacked beams and posts, which can place each purlin at any height.
The rules it illustrates
The hidden roof: separate the eaves from the weather. Build the visible eaves as low and wide as the design requires, and above the visible ceiling raise a second, steeper roof on cantilever beams (hanegi) to shed the rain.
Tie the feet of the rafters: the truss. To roof a wide span, join each pair of rafters to a tie beam at their feet so that the three form a triangle that cannot spread; hang the tie beam from the apex by a king post, or by two queen posts on larger spans.
The raised-beam frame: purlins at any height. Instead of a triangle, stack beams one above another, each shorter than the one below and raised on short posts, and lay a purlin on each beam-end; the heights of the purlins then set the section of the roof, which may be curved at will.
Where it appears in the book
In the chapters The Roof.