Is this Your homework?
What type of robot would it look like ?
It would look the way You want it to look. If You build a robot, You decide upon its looks and functionality (which would influence looks).
How complicated will be robot be ?
As complicated as You want it to be, or as complicated to successfully perform given task.
Does it open up possibility to evolve robot like biological creature ? (Darwin evolutionary theory survival of the fittest )
It does not as to achieve that robot has to be able to think and we all know that true artificial intelligence does not exist
What would be the end point of the robot after evolving using the basis as survival =able to collect energy on its own ?
To start with, robots cannot "evolve" by themselves as they do not posses true artificial intelligence, hence no cognitive thinking. They cannot set own goals apart from the ones that are set for them by humans.
Suggestion to implement self assemble robot ?
"Self assembling robot" and "evolution able robot" may be very different things. "Self assembling robot" can be simple ABB robotic arm assembling other ABB robotic arms, or it can be a robot with some clever algorithms which identify broken parts and actuate robot in proper sequence to obtain new part from the stock-room and replace the broken one with it. If, however, You are talking about "Matrix"-like robots - they are only Sci-Fi yet (if possible at all).
How to assemble a robot using the same robot ?
You need to create robot first in order for it to perform something, as soon as it completes the job - it stops, unless further instructions are given. Robot cannot build itself from noting, there has to be a starting point. Even for such advanced organisms like humans - it takes 2 to make 1. And even if scientist come up with some synthetic cell based materials for robots which would be able to split and grow colonies the same way Your flesh does - robots would still lack human-like dreams to motivate them to do something apart from what's been told for them to do.