In this design the foundation is lower than the pet door. I recommend placing the pet door level with the foundation though it can be in many places.
The measurements of the existing conditions of where the Lanai is to be installed is the first step in designing the foundation. The design of the foundation influences the design of the Lanai mostly in the placing of the receptacle pipes. The overall shape and design is build around them.
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I also welcome inquiries from professionals interested in learning more about my Lanais with the intend of getting included in my Installer List.