The message
from SusieThompson contains these words:

We are thinking about buying a 10x10 polytunnel for our new garden -
this is the largest we can fit into space available. It will be
situated on the southerly side of our home, and will get no shade at all
during the height of summer, but some shade in depths of winter.

The other option is, of course, a greenhouse,


Note to the original poster:

A friend has been considering buying a large polytunnel for some time.
He happened to pass a house the other day that had an old aluminium
greenhouse in the untended garden. It was a large greenhouse and some
of the glass was missing. He knocked on the house door and made an
offer for the greenhouse. He got it for 60 UKP, a bargain! He then
went to a DIY store and bought another greenhouse, smaller than the
second hand one, (in order to make up space that he would have had in a
large tunnel) and got home to find that they had given him the galss
package for a much larger greenhouse. He now has enough glass to glaze
both new and second hand greenhouses - lucky blighter! Anyway, point of
the story is that there may be a good quality greenhouse or tunnel
nearby that could be bought for a song.

--
Cheers,
Compo