Hi Graham
I agree with Sproket,the windows position is critical,we have bought porches from ebay and sometimes you can get previous years models at good price,from personal experience IsabellA would be first choice for quality but you will pay a premium,they also own the Ventura brand and the quality is good also,we currently use a Quest porch, which is made in China and the design was obviously 'inspired'by Isabella,wh bought ours new and about half the cost of the new Isabella Magnum,it has choice of steel or alloy frame,and lots of useful features.Your other coNsideration could be roof shape,some have apitched type roof,and some have plain slope,I would advise a visit to a dealer with a good awning display,take a tape measure and see for yourself.When you find something suitable have a look on ebay and get an idea of the costs involved.