A few years ago my parents had a pitch (plastic) roof on their conservatory, it was too hot in the summer and to noisy in the winter with the rain drumming on it and started leaking so it had to go!
Best long term option was to have a aluminium roof frame and lightweight roof tiles tiles added, no need to worry about foundations as it’s designed for this purpose.
Here’s some pictures of their conservative when finished, they opted for the high ceiling (without Velux windows) but you could always have a ceiling level to match your other rooms.
If you need any info I can always ask my dad who did the work etc.
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