Frederick Williams wrote:
Can anyone recommend web sites that instruct one in the building of a
greenhouse?

Not really.

What I would say though is think long and hard about the glazing.
The cheapest (horticultural glass) is easy to get as a replacement but
when it breaks it breaks into long jaggy pieces of glass (dangerous).
The dearest (polycarbonate) is hard to get. We got toughened glass as
youngest was in danger of 'piling' through the glass and this shatters
into lots of little pieces, it is really quite strong when loads are
placed on it but it is quite delicate at the edges, and will shatter
rather than crack . I wish we had gone with a polycarbonate system or
laminated glass and hang the expense. Frightened to look at the
greenhouse (probably unnecessarily) in case one of the panels goes as
the whole panel will need replaced not just a crack taped or some such.

So if NO chance of children animals etc breaking the glass probably
ordinary stuff will do (after all it has worked on windows for hundreds
of years)if at all worried go for an 'unbreakable' method and hang the
expense, do not choose the halfway house (like I did) of toughened glass.
All IMHO