I want create a root partition and a home partition. for a 216 GB of secondary storage, how much space should I allocate for the root partition and for the home partition?
This site is for the co-ordination of the Ubuntu project(s), and not support. Sorry.
This sort of question has been asked in the support venues at https://community.ubuntu.com/t/finding-help/712 many times, and we hope the many answers there seems sensible to you.
Many new users experiment with several different partitioning ideas before settling upon a daily-use concept, so backups are important!