Recently my co-worker paid me to make her some custom books. She wanted two in the same dimensions as a lined notebook she already had, but one which had plain paper so she could write in it horizontally, and one which opened at the short edge to form a very long, thin double page spread. That one also needed heavy paper, so she could paint in it if she wanted.
It was a lot of fun making something different to my usual A6 notebooks, but cutting the pages to a custom size left me with a lot of off-cuts. So, naturally, I made those into books too. I got four mini notebooks out of them, in two different sizes. (I photographed them with an A6 book for comparison.) I'll have the minis to sell at Manchester MCM later this month.