Looks like the firepit is made from sleepers.
Our burner generates a lot of heat under the burner, hot enough to burn wood. There must be nothing combustible inside the pit under the burner. Also the metal burner tray will become red hot during use, so it must not touch or be supported by wood.
Also, I cannot see any ventilation holes in the pit. I hope there are some round the other side. Without adequate ventilation the inside of the pit will become too hot, and the burner can fail. With all that wood around, you really don’t want that.
If installing a firepit in an open sided gazebo, you must allow the heat and fumes to escape up through the roof. If the roof does not have ventilation, you could install a decorative canopy above the firepit, to allow the heat and fume to escape. See sketches showing the basic concept.