I want to replace old PVC single door and side windows by removing dwarf wall and installing a 4 metre run of aluminium sliding doors with new access door. Al this sits under a Polycarbonate roof in my sun room. Current lintel running above all glazing is just 4 x 2 timber. What lintel will I need to replace the old timber? Aluminium hopefully? Where can I obtain such a lintel? Will I need to build a supporting 'pillar' to support the new lintel at end of removed dwarf wall. The other end would sit on a standard 9" cavity block wall. Retired with time