Dear Abhay,
Preparation employee handbook is the activity that has to be handled by the senior HR professionals. How come they have delegated this important work to a rookie like you is not understood. Your association with the company will be for a small duration. It appears that principles of delegation stopped at the doorstep of the Head HR of the company where you are doing internship.
Anyway, search this forum. You will get material on this subject. Look at the right side of the post and you will get the posts are relevant to the employee handbook.
Thanks,
Dinesh Divekar