I got a better deal by going to a local manufacturer of windows/conservatories, had them make what I wanted.

Quality was superb, had help when I needed and anything I required surplus to what they supplied initially they had in stock which they brought round to the job.  Since then I have always specified and used them for porch panels and windows.

Just a thought for you to consider,  I am quite lucky that I have two local manufacturers.  They do take some finding though!!

I built a Wickes one a few years ago, it was pretty straightforward, just make sure the base and any dwarf walls are absolutely square and level.