Ive been reading more physics lately to try educate myself better and some have some questions. I presume this is different depending on the material and structure of an object, but I was wondering - the earth is essentially an incredibly smooth sphere, caused by gravity which pulls all the components of it equally from all direction towards the centre.

How big did the earth need to become before this effect started to be significant.

How big would a metallic structure like a space station need to be?

How "far" would you need to be from other gravity sources before they wouldnt affect this. (Obviously this varies with other sources mass, but rather , what level of gravity from other sources could you tolerate. )