From the start – Plain Red Deal timber screwed with brackets and back supports.
The second pic – took some time with planes and some tools just a wee bit more complicated than a saw and screwdriver (but not much). Still Red Deal, but I wanted a long span of shelves without solid uprights, so put in rebated edge pillars.
The third is saw and screw again, but this time I got my hands on some Oregon Pine. Very solid but light board with some boards very wide. Beautiful smell when you cut it (imho).
The last picture is medium density fibre board that is double sided carolina pine veneered. I faced it from red deal. The bookcases started as an 8’x4’x1/2″ sheet and a 9″x3″x18′ length of Red Deal. This was done on a course I took – basic cabinet making.
I still have some boxes of books to go up, but getting there! The Trinity booksale is over for this year so I do not imagine any more massive influx of books at one time for a few months. Time to perhaps make more shelves.