on the above plan for making the polytunnel i tried to make but found that the water pipe was a little flimsey but i strengthened it up by screwing a light wooden frame on the inside of the pipe ill have to get a picture of the finnished thing for you
I then used First poly tunnels (
http://www.firsttunnels.co.uk/) and ordered my Plastic cover (mine was 14ft by 8ft and required a piece 9.3m by 7.2) if you put your measurements into the above link itll work it out for you (it also allows you to either bury the plastic to hold it down or you can buy pieces specially for holding the plastic into (its starts to get a little pricey)
i just wanted something that resembled a polytunnel and to be fair its prettyy neat and been admired by far and few across the Allotments
i made sure that all the surfaces where covered with duck tape(there are cheaper versions that do the same job which i aquired from B&Q bout 6 quid i think it was for the tape the plastic cost 45quid and the rest i either begged borrowed and well not quite stole lol
it took me about 3 days to complete mind you i still have doors to make !!! one end is presently covered in with a nice piece of perspex that i found
ow another good point is that i grow my tomatoes on sand which is a little easier to handle than soil !! (a commercial grower gave me the tip)
any way have fun if you go about it that way
carl
ps if you need a bit o advice then do leave a message