Our Folding sliding doors came from The Folding Sliding Door Company in Yorkshire. I ordered them in early Novemeber 2010 and they were delivered early December. The company advised that the doors could be fitted by any decent DIYer and so I did them with the help of my father.
There were some annoying things to be addressed like the fact that the Catnic (steel beam) over the opening was not level - about 1/2 an inch out over its length (I wish I had noticed this before I had put the roof on or in fact before the builders had finished) and the fact the there was a slight slope to the floor the other way - though not much.
These things meant that we had to do some extreme trimming to the top track (thank heavens you can cut aluminium with a suitable router bit) and both the side verticals needed about 1/4 an inch taking off them - this was partly down to my measuring as well - I did not make a mistake as such but I should allow more on the width and not assumed that my sides were perfectly vertical.
Anyway, we got the doors installed and working. I have since added some magnets to keep them together when they are all 'stacked' open and I am very pleased with them so far.
The following little movie shows them working soon after they were fitted.