>>2715113>roof optionsMuch depends on the tools you own. Do you have a welder?
Do you consider buying structural steel, or do you have some leftovers from shrinking the gazebo?
Can you bend metal rods to insert them from the top of the vertical profiles of the greenhouse?
Flat roof is not a good option, for leaves&dirt that falls on top won't be flushed down during a rain, and it's rarely flat enough not to leave dirty puddles.
You can go with foil for the triangular sides of a pyramid-shape roof, which would be an easy solution.
You can make a gable roof or shed roof, as pic related. Fastening the top surface plastic to a frame and using a hinge will let you open the roof on heat strikes. It's easy to reuse some fasteners from some old roof window to this end. Triangular sides for these roofs can be done by cutting rectangular plastic pieces diagonally, so it's not that big issue.