Sorry about the dalay - had some work commitments.
Thanks again for that, very valuable advice.
On the face of it, it doesn't seem too difficult to do, apart from lots of screwing!
The ditch is at the end of my garden, unless you meant where in the country is it, if so it's in cambrideshire - too far for you i think.
I have a friendly builder mate who is going to try and get me a good deal on the timber - so it looks like it's full steam ahead!
Thanks so far - I'm sure they'll be more questions!!