A friend has used redundant secondary double glazing to enclose the two foot veranda of his shed and uses it for his cacti.
These are large single glazed plastic frames which slot into U shaped (sort of) channel screwed to the concrete path and wooden overhanging roof. Nice and snug, well-sealed, also easy access as the panels slide in the channel.

He is a bit of a d.i.y. god , mind.

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