How to make my villager trading hall look less weird, i like the shape but it looks so plain and weird. Any Ideas?

Add some colorful banners or flowers to spruce it up!

Second floor balcony or window? If not that then something to add dimension or texture to the upper part of the build. Perhaps some pillars for dimension and throw in a few variants of deep-slate for some texture.

Do a pixel art emerald where that empty space is

Windows.