There is a unique manuscript called "The Sketchbook of Villard de Honnecourt." We know nothing about Villard except what can be gleaned from the internal evidence of this manuscript, which seems to be a notebook of his travels and interests. MS Fr 19093 now is in the Bibliotheque Nationale in Paris; it has been extensively copied and studied since it became widely known in 1849.
Still, he seems particularly introduced in buildings, drawing detailed façades of Laon and Reims Cathedral, a clocktower, the geometry of buildings; but he also depicts animals and insects, sculptures and mechanical devices such as a trebuchet, a machine for lifting heavy objects, a self-operating saw, a crossbow that never misses, and a perpetual motion machine. Alas, he draws them without explaining how to make them work.
Sketching guidelines was not an unusual start for medieval artists. Villard, however, offers us several examples of the correlation between geometry and representations of organic figures. Shown to the right is Page XXXVI of his manuscript, in which he shows how geometry fits into faces and figures.
His note in the bottom of the page depicted here says "Here begins the method of representation as taught by the art of geometry, to facilitate work. Elsewhere you will find the method of masonry."
A brief video showing some of his pages is here: