The message
from Tim Tyler contains these words:

/snip/

If the structure is of any size, the lifting would be a
progressive process - using a mixture of ropes from the outside,
stakes to pin in the far edge - and perhaps props from the inside.

I think it even makes sense put the polythene in place (and
hold it there using pegs along the edges) while the structure
is lying flat - only battoning it down after erection.

/snip/

I haven't got round to looking at your pages yet - but I will. I mention
this just in case you've suggested this...

Have you thought of pegging (preferably burying the bottom of) one edge
of the polythene and folding it away from where you are having the
tunnel?

Construct your lattice on the ground where the tunnel is to go, then
erect it, and afterwards, pull the membrane over it?

It wouldn't work in my garden, as it's far too narrow to lay it flat,
sensibly, and is somewhat - er - mature.

http://www.users.zetnet.co.uk/hi-fi/garden.htm

It has been tidied up a bit, but things will keep growing, despite the
best efforts of the resident molluscs.

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/