I've been making my own sketchbooks for at least six years now. I've filled up dozens and dozens of them. Most are made from lettersized paper, cut in three, then folded over. This is the ideal size to fit inside my back pocket.
They contain on average just 30 pages or so, so as not to be too thick. I use regular office paper, and a bit of cardstock for the cover.
Sometimes I make a fancy cover, sometimes not:
Here's some covers up close:
I make my own because I want them to be cheap. So cheap that I'm not afraid to fill them with bad ideas and lousy sketches (my little books cost about 15 cents each to make). A nice, brand new leatherbound (not cheap!) notebook is intimidating for me. I'd want every sketch to be lovely and perfect. I'd want only my best ideas to grace its pages. In a nutshell, the preciousness would be too restrictive, and put a damper on my creativity. It would put a filter on my ideas. Not good.
I need to make loads of mistakes. I need to go to the edges of what makes sense. I need to fly without a net. I need to be quick and messy and just get the ideas (and mostly nonsensical things) down as they come to me, and worry about composition and details later.
I get my ideas from everything and everywhere. I carry one of these sketchbooks and a pen with me at all times, so that whenever an idea comes to mind I can get it on paper. I might be in a lineup at a coffee shop, on the bus, watching TV, or putting the kids to sleep. I’ll overhear a conversation, see some quirky signage, spot an interesting pattern, or think of an odd combination of objects and I’ll pull out a sketchbook and get the idea down on paper. Sometimes an idea for a drawing shows up in my head all ready to go. Other times it's just a single word, sometimes an object, a layout, which I come back to later to flesh out into something more complete.
Here's some inside pages:
Having one of these on me at all times eventually takes a toll on my jeans. Take a look at the back left pocket on this old pair:
When I'm not sure what to draw, I'll rummage through a pile of old sketchbooks and hopefully find some decent ideas. Maybe it's a tidbit I scribbled down three years ago, and at the time it was just the beginning of a drawing. But I'll come across it today and it'll spark something and I'll polish it and add some new text and turn it into a finished piece.
I'd be screwed without my stash of sketchbooks. They're such a huge part of my process.