On Sunday, 1 October 2017 12:06:31 UTC+1, GB wrote:

I'm not sure that I would trust all that weight to a wall that was not
built with that in mind.

You've got me thinking - I was assuming a conventional tiled roof just to directly match the house and garage roofs as per the following pic (showing the latter at least; I don't seem to have a photo of the whole rear but the same pantiles are used on both):

http://www.newtonnet.co.uk/permanent/conservatory.jpg

Do you/anyone have any alternative ideas with regards to the roof - perhaps something lighter but still obviously satisfying the necessary U-values and ideally not something that belongs on Grand Designs, both in style and associated cost! Due to (lack of) light in the existing lounge we are intending to put rooflights in this lean-to and so it would have to be compatible with those.