This Gazebo was created from parts from the Bioshock Infinite gazebo. I just went with the "It looks good to me" plan rather than the "correct" assembly.
Gazebo mesh extracted by theoneman.
I retained the footprint of the "Blushing Beauty Wedding Arch in order to allow objects to be placed within the gazebo. ((Which means Sims will be able to walk through the walls unless you block them.) I suggest placing the gazebo on an octogonal foundation as in the picture.