UE4 must have a tool which will build particular selected area only

[KVogler]

for that purpose that tool should be there or it should be like Maya whatever is in the camera view it should render it so we can see the rendered image and then saving it to compare it for another render image.

Render viewports of 3d apps like MAya, max and co work quite differently than those in a game engine.

wanna say why do I need to build the whole scene I could just render that image and see it as image

Because what is on your screen depends on things ouside of it…