For a long time I had considered using trestle frame construction for a greenhouse, the internal framework is heavily braced owing to the numerous triangulated sections. And it is simple- a series of trestles with two rows of beams extending as long as is needed. Fundamentally, virtually all structures follow this vertical post and horizontal beam layout, only here it is reduced to its essential features. The basic unit shows a heavily braced right angled hexahedral polyhedron (a cube, more or less).
Recently I was reconsidering Roald Gunderson's log buildings (see also here), where logs are used in place of dimensional lumber. He built a greenhouse that resembles a very primitive longhouse - one beam, supported by a single row of posts, and a gabled roof with low or absent walls. Although in such a design - kingpost columns supporting a central beam - the amount of cross bracing appears low when compared to trestle frame buildings, there are three cross braced sections in different planes that support one another. In fact any two of the sections can support each another, providing more than the minimal needed for a tripod. The kingpost (third section) adds structural support and permits easier construction.
The simple design of a kingpost supported A-frame with its single beam and row of columns can be very beautiful, as it is in the hands of Roald Gunderson:
Leaf House featured on pp. 18-19 in Builder's of the Pacific Coast by Lloyd Kahn. It is the simplest of all - a single beam at the ridge of the roof balanced on a single post.
Considering this variation on longhouse design has provided me with a more appreciative perspective. The utilization of posts, regardless of position within a building, is interesting. Here is a very simple central post in a building that may have branching supports in tree-like fashion - a more three dimensional aspect than most standard two dimensional trusses. The image comes from pg. 175 of The Barefoot Architect: A Handbook for Green Building by Johan van Lengen.