First, a little deduction: The question's confusion between /root (the root account's directory) and / (the filesystem root directory, which has nothing to do with the root account) suggests that you are a new user.
The phrasing of the question suggests that you are in the process of making a classic new-user mistake: Over-planning and over-partitioning. Your previous Windows experience will generally lead you to wrong answers, since Windows and Linux work quite differently.
Advice #1: Make your first install successful, not perfect. Keep it simple. Go with the installer defaults, even if they are not quite what you want yet. Once you can successfully install, then turn-round and use your experience to re-install with the customizations or additional complexity that you want.
Advice #2: New power-users coming from Windows often love that Linux distros let you see and poke all the spinning gears. However, poking your finger into spinning gears will injure your finger and break the machine. So keep your hands in your pockets and don't poke something until you have researched what you are poking and what the consequences are. And keep proper backups so you can restore the machine when you break it.
Advice #3: Many new power-users who customize their install decide to backup-and-repartition after a few months of experience. Their partition usage sizes don't match their original estimates, so one partition is full while another is nearly empty. Be prepared to admit that your guesses about the future might not be accurate predictions, and prepare accordingly.
Advice #4: Most laptop users suspend or hibernate rather than fully poweroff or reboot. With longer battery life, I've seen suspend replace hibernation among my peers. So maybe a /boot partition on SSD is important...and maybe it's not. Keep in mind that the /boot partition contains ONLY the Linux kernel --and not the many GB of the rest of the operating system-- so putting it on the SSD may not speed your boot as much as you hope. You have all the tools you need to try /boot on both SSD and HDD, to time each method, and make your own decision...if you know how to use those tools.
Advice #5: For most general-purpose users, 16GB is plenty for everything outside of your /home directory. /home is where you store all your movies and music and mail and other voluminous data. So /home on the big HDD and everything else on the smaller SSD. Try that simple configuration before diving too deep into more complex alternatives.
