I've just had a look at the video in your link, Ratts. Looks like an excellent system. No loading problems with such a lightweight roof structure. I was surprised at the high level of insulation they use.
The only issue I can foresee is the cost of course. It won't be cheap, but then nothing is.
If you do find the cost higher than you anticipated, it may well be worth asking a builder to quote for a traditional structure. That's what Jack was talking about.
Traditional is not lightweight. So, additional support would be needed. This needn't be onerous. With a simple, rectangular shape (as in the video), structural posts could easily be introduced into the far corners. These would carry edge beams that would be carried at the other end by letting them into the building.
Even with "threepenny-bit" shaped concervatories, it would just need posts at all the pointy bits of the shape to carry more edge beams.
Once that's done, a traditional roof structure (timber) can be cut and fixed, with a regular roof covering to suit the rest of the building.
It would be interesting to see the comparison figures between trad and lightweight.