I designed this bookcase to be compact and moveable. Basically, it's like a trunk on its side. The books will only be accessible when the door is open. I did it this way to keep dust and moisture out and also allow the casters to sit further out when closed. One side will be anchored to the wall, because I don't need to roll it around yet.
I was thinking of using 8 to 12 or so 1-5/8' tall casters per piece (16 or 24 total), but I'm not so sure of what sort of hinges or locking latches to use. The casters sit about 1/4 higher than the base of the frame, so that I can slide in some wedges on the anchored side to keep it from moving. I might just forgo locking latches and use some ratcheting straps if it needs to be moved. I'm also unsure if there are any design flaws, but I guess my main concern is how well the 6" deep frame will hold up to flexing.
Most of this will be cut from 12' x 97' x 5/8' particle veneer boards (white) and MDF boards (brown) of the same size. I forgot what the thin backboards were called. The shelves will be screwed in on the sides. I'm not entirely sure how to affix the center support columns. The base will be double thick, so that it is more stiff and so that the weight is distributed more evenly onto the casters.
I guess it would be easier to fix the center columns and base if I used MDF all around, because I would be able to glue it more effectively.
alternative 1: use tracks to slide front shelves, while rear remains fixed.
alternative 2: use 12' deep shelf and skip gimmicky doors or tracks, but it will still be on casters.
shelf length is easier to cut, for me, if it's half of 72' or 97'.