How large should the terrace roofing be?

But I would still not recommend installing opaque canopies in front of windows or patio doors.

Above all, one should not install opaque canopies over light wells. Realistically, I only see a glass roof as an option for the OP.

I thought so too at first, but does he perhaps mean a glazed recess in the canopy? Because there is a window at that spot?

The time window during which the light falls through the dome into the kitchen is probably quite short. In the west/in the evening, the sun is lower and that makes the whole thing even more unnecessary.

Take a look at comparable roofs among your acquaintances.
What speaks against all-glass?

We decided on the short terrace roof last year and in hindsight should have chosen the long one.

Under a glass roof on the south or southwest side, it can also become very oppressively hot, especially since one side is closed off by a wall anyway. I find the shorter version more aesthetically pleasing. The question is also: do you want a terrace area that is not covered, so it receives all the sun and weather? This can certainly be desired, for example to sunbathe on a lounge chair without sitting under the roof or to position plants there without having to water them constantly because they don't get any rain, and so on.