The shape of an interstellar space ship would be determined by several factors. If you have an engine at the back end that may be hazardous to the crew by the production of ionizing radiation then the crew would need to be as far as possible from it as other safety considerations allow. The space ship would need to be of such a shape that the thrust from the engine passed as nearly through its constituents as possible so a to minimize the amount of structural materials needed. This gives a long thin structure with in order from the front particle shield, water tank, provisions, accommodation, fuel, engine. By being long and thin there is less chance of collisions with particles and the crew is as far away from the hazard of collision and engines as possible. It would probably look like a radio mast or tube with lots of bits bolted on the outside, so that they could be jettisoned if needed, an engine at one end and a shield wide enough to protect the essential bits at the front. This layout has been re-invented many times.