Instead of using like 3d cubes to build maps use probuilder like make a flat ground, put on the third tool on the top of one of the probuilder tabs (Also that's like on top of where you add stuff like the scene), then grab the lines on the edge of the flat land while holding shift, and then press control and at the same time, then get the scale tool and scale it up, from then go to the unity tools the ones in the right and look for a button that says like fill something I think it's in like red. Also, Idk how else to explain this better so if it's confusing to you then just search up like how to use probuilder.
