How can I add a new fixed wing drone geometry into PX4?

I’m part of a student team, and we are building an autonomous, solar fixed wing drone from scratch. It has unconventional geometry, and we want to implement it on PX4 and then simulate it on Gazebo. How can we implement a new geometry on PX4? I read we have to create a new airframe, but can you explain to us how to do it step by step?

it depends on which Gazebo version you are targeting:

Gazebo Classic

New Gazebo (Garden)

hey @Jaeyoung-Lim is this correct?