I know what they are called, that will help me. So far I can find
people wanting to sell me their gates, not help me make my own. I can
see pictures on their sites showing the arrangement of the timbers but
they do not share the trade secrets of what size the timber has to be!

I'm bored waiting on a phone call so....

you might look at http://www.nc-web.net/sandpjoinery/products.html
(advertising wooden field gates up to 5.6m; level crossing gates up to
13m) or http://www.jamessmithfencing.co.uk/c...ub.asp?page=12
(metal gates to 16ft).

(that you contemplate DIY-ing such a gate makes me feel more than a
little inadequate)
--
R