Initial layout (without dialogue box):
I started by studying the progression of Civilization diplomacy screens over time.
I noticed that the list of items the player could offer, and the items the NPC could trade in return, were on opposite sides of the screen in earlier Civ titles, but moved to the same side with Civilization 6.
This layout makes navigating and consuming the information a lot less strenuous for the player in my opinion, and I wanted to start by building off of this layout.
The active trade proposal window is given more width in this design to emphasize its importance in the trade process.