As you can see, I think it's the shadow, makes my textures look like something where a nade has been throwing against. It looks ugly Cause you can see all the line how the building is made, is there something I can fix this?
You can make the walls detail. Lighting affects detail brushes differently. If it's a dummy building, make that wall thicker. If it's not a dummy, make the walls a sandwich, with shadowclip in the middle. No guarantees any of these will work... Q3 engine is notorious for lighting problems.