Any reason you can't carefuly remove the glass? Sorry if you've already
ansered this - only saw the end of this thread!

If not, try buying a glass cutting tool and scoring each pane with a cross
beforehand as this will encourage the glass the break into largish pieces.
Then hit it gently (full protection of course for you!) in the centre of the
cross and from the other side - so score the INSIDE and hit gently inwards
onto the groundsheet/old matting etc. that others have suggested.

Start at the roof (obviously) and work downwards.

FYI, I have managed to dismantle an aluminium greenhouse, losing only two
panes of glass. You just need to be slow and methodical and if you are
going to reuse it, or know someone who can, mark EVERY pane of glass with a
unique number and sketch a plan before dismantling anything. Thanks to a
friend and a couple of summer afternoons, I got a nice greenhouse for next
to nothing.

Take care!
Paul DS.