(Actually, I've never gotten a question exactly like this about the Book of Shadows before, but one neophyte rolled several questions I've had before into one inquiry.)
Answer: I think I need to explain some things first before answering where and how I acquired what.
Most 21st century Wiccans do not inherit a BOS. There’s an old story that claims the secret BOSs were always burned when a Wiccan died. (I tend to have my doubts about how true that bit of Wiccan lore actually is—but that’s more of a history discussion.)
In a Wiccan coven, each initiated coven member will keep her/his personal copy of the coven BOS. This BOS may have to be hand copied from the coven BOS. However, this info may also may also handed out to coven student as photocopies or computer printouts.
Someone who is studying Wicca, but has not yet found a coven, may assemble or create her/his own personal BOS sometime before entering into a coven when s/he begins Craft studies. Even after s/he enters a coven, s/he will likely hang onto this old personal BOS. A student might even start a new personal book that incorporating teachings learned in the coven and new insights with learning and personal practice. One never really stops learning—even when one has gotten the basics down.
I’d been scribbling stuff into books for years, before I finally connected with a coven in the mid 1980’s. I received a BOS from that that coven, which I still have. Many years later, I initiated into another tradition and I still have that BOS.
In between, I’ve continued copying and writing stuff into notebooks, webpages, etc. on dozens of subjects related to my personal practice. This information has gleaned from many published books, friends, open community rituals, etc.
There is no one definitive Book of Shadows (BOS). You'll find that a Wiccan BOS can come in many shapes and sizes and styles.
People often buy a journal book or notebook and write stuff or cut and paste stuff into it from either their teachers or the internet or published books on Wicca, Magick, Mythology, and Mysticism.
Should you make your own personal BOS?
You certainly can—if you wish. Collecting, writing, and organizing information is great way to assimilate it into your understanding within your own mind.
For practical reasons, three-ring binder notebooks are commonly used so pages can be added, updated, or rearranged as needed. However, I know some people also use very beautiful bound journals. Click through links to photos below.
What should you include in your own personal book?
If you want it to serve as your personal BOS, you probably some of the following: Rituals for moon circles (esbats) and seasonal circles (sabbats). Spells and magical theory. Ethics. The Charge of the Goddess. Deities & Spirits. Directions for casting/erasing a circle and calling and bidding farewell to four directions. Something about herbs. Moon phases. If you like stones and crystals, then something about stones…Pretty much anthing you think will be useful to your practice.
You should read Jason Mankey, The Witch's Book of Shadows: The Craft, Lore & Magick of the Witch's Grimoire, 2017.
You should also check out some photos I have collected of sundry BOSs:
BOS A
BOS B
BOS C
BOS D
BOS E
BOS F
Further reading: Patti Wigington, https://www.thoughtco.com/make-a-book-of-shadows-2562826 How to Make a Book of Shadows 2014, 2017, accessed 9/27/2017