I have never considered making my own journal, but after seeing how easy it is, I may just try it in the future. There are a lot of other instructions online that look helpful, but before looking I would recommend deciding the basic materials you want to use to narrow your search. A homemade journal can be anything from a large, intense bound journal to a few pieces of paper carefully tied together.
Image courtesy of andchristina
Image courtesy of it's not so easy being green
Image courtesy of Serena3116
If making a journal seems like too much work you can also decorate one with fabric, painting, markers, or just a few inscriptions.
Image courtesy of A Beautiful Mess
For instructions on how to make a fabric covered journal, check out this post as well as look for more instructions online.