I never thought about a rooftop pool except in a commercial application. However, it appears that they do exist! Here are a few inspiration photos that you can click though to the product info that might help you (at least a starting point for research)
https://www.houzz.com/photos/402-redbud-contemporary-pool-austin-phvw-vp~26601

To get it to extend, you might have to do something like this one

Thank you very much. I was thinking along the lines of this photo.....

Beautiful! You definitely need an architect/engineer. I can't imagine how heavy that load is with the water. It certainly is an outstanding look.

Thank you for your input. Agree on the weight; knew it would to be a lot of tonnage with the water etc. Ideas were wanted to give to the architect so they could see what was in mind. Not looking to have the glass in it but the idea of building it out is key. Thanks again.

If the pool is going on top of a structure or elevated, my suggestion would be to look in to stainless steel pool shell with a supporting system of steel girders. This a common building practice in large cities such as New York. It works well and allows for movement without cracking the shell.

Hello. Hope You are still using this platform. I am planning on doing a project for my cousin and he wants a pool above six garages. The pool starts at the third garage and ends at fourth one. It is 4x5 m and starts from 80 cm depth to a max 1,2 m. Hope you could give me info about Your project and how You solved load distibution. Thanks in advance.