Here is the 5th in a series of articles by Jack Sobon, timber framing book author.
In the design of timber-framed buildings, the roof is the dominant element. The structural system necessary to support its expanse greatly influences the total building design. In masonry buildings, the roof structure may be the only timber-framed element. The carpenters who timber framed America hailed from European countries where roofs were predominantly thatch, tile and stone. In America, the abundance of excellent timber and the economy of working it led to a preponderance of board and wood-shingleroofs. The timber quality also affected the framing choices. In Europe, efficient use of timber was essential. Timber-framed buildings included members of all sizes,shapes and lengths, making the best use of the forest. Here, time and labor constraints dictated timber selection. … (found on scribd.com)