A modular greenhouse construction in which panels are prefabricated from a universal beam or mullion and the panels are interlocked to form walls and a roof. The universal beam has a spline receiving groove in one surface and a ribbed channel in the surface opposite with C-shaped slots on either side...http://www.google.sh/patents/US4057941?utm_source=gb-gplus-sharePatent US4057941 - Modular green house construction
