For the lid, I was thinking about something like this...
Rail is simple galvanized 50x5 bar (Bunnings), 5m long (it will have to be made from 2~3 pieces).
The frame will be made of 70x35mm treated pine timber, covered with corrugated roofing (polycarbonate? or colorbond.. not sure yet).
It will have to be insulated from below, to avoid/minimise condensation.
I plan to use (Bunnings)
garage brushes at edges to minimise wind coming inside.