Structural design for timber frame extension to UK building regs

I'm requiring structural calculations for a single story extension mono pitch into flat roof. Design to incorporate solid air dried oak bottom cord and vertical posts to support treated softwood rafters and flat roof joist. The extension walls are to be built with 5x2 @ 400mm centres with 18mm OSB sheathing and external brickwork. Associated lintel design for window and door openings also required. Project is subject to UK building regulations.