Abstract: A prefabricated post and beam lean-to or free standing structure, incorporating a self-aligning, load bearing mortise and tenon joint assembly which results in a mitred joint with no visible hardware when fabricated. The structure is formed from a plurality of post and beams arranged in spaced, parallel, vertical and inclined. Attitudes extending from a lower support surface at the base of the post, with the inclined beams attaching at a higher support surface. The prefabricated sloping mortise in the post allows the beam's prefabricated tenons to be modified, on site, to descend further into the sloping mortise channel enabling the slope to be adjusted. This frame system then supports single or double glass or other sheets of material for lateral support over the enclosure.