Those crystal clear corrugated plastic sheets are used for roofs and are really cheap. I buy them to make ceiling to floor lighted bubble sculptures.

THey can even be turned into a cylinder.

I have some tent gazebos that I am thinking of adding durable cheap wavy plastic sheets on the roof and sides to make a greenhouse.
With a center pole and good bracing on the ground the structure has been sound for 3 years so far as a tent gazebo.