Why is the lighting on my model so messed up?

Hi,
I modeled a simple house, but the lighting is just broke on it. I wonder why? Tried everything that came to my mind, but it still looks broke af…

Anyone? As you can see the shotgun is doing fine…

in the object import settings enable “Generate Lightmap UVs” Ideally would be to have the lightmaps uvs placed correctly from your 3D app but most of the time that setting will work fine.