As I recall it is about 18 feet wide x 16 feet deep. There is a fireplace in the center with built in seats on either side and counters on the left and right hand sides - one with a small kitchen area, the other for serving. the pool was existing and a side yard setback determined the depth of the cabana.

ready to build, can u tell me the size of the window and where i can purchase?

They were "found" windows and I do not have the exact size. Apologies. If you need specs for building I would recommend you engage an architect to design for you. I think personally it is a bit chancy to base your cupola on a photograph of another design that may be sitting on a roof and house that is not the same scale as your project. I am not trying to be critical of your process, but this is the reason to hire a professional. I regret I don't have the specific sizes, as I recall, they were from the top and bottom sashes of a discarded double hung window that I incorporated in the design. This project was constructed over 12 years ago. I wish I could be more help. I don't know the current owner to even ask them for permission to measure. The previous answer to your inquiry was an estimate, not imagining it was the basis of construction specifications... more a reply to a general inquiry regarding the approximate size of the cupola.