I need a bookcase(s) for just paperbacks. Any ideas

Buy a cheap standard bookcase.(Ikea?) Usually 11 1/2 to 12" deep. Take it all apart. Run each peice through tablesaw to get your 6". Re assemble, adding a few pin nails or fasteners of various kinds to replace those cut off in the cutting down process. And you will have 2 Custom bookshelves. Find another Paperback bookworm. Sell them the extra one for the price of the 12 inch unit, and you have a free bookcase AND a fellow bookworm who owes you a favor.

Have you checked out thrift stores? You'd get it for a very good price an people are forever getting rid of things they no longer want and need. You'll probably find exactly what you want, or perhaps you can make one yourself, it wouldn't be hard at all.

https://www.pinterest.com/pin/108227197275709578/?lp=true

Find a shelf for VHS tapes or DVDs. They fit perfectly.

You could make your own. Most big box hardware stores will cut the boards to the length you need. Draw up a plan so you can figure out what size boards you need for the sides and top and number of shelves and how deep they need to be. Pick out some boards that are the right width (some won't need sanding if you are careful in which boards you pick out) and have them cut to size. You will need a back to stabilize the bookcase and you can use

1/8th inch plywood cut to the size of the bookcase. Assemble using nails or (preferably) screws then stain and varnish, or paint. Let dry for several days to a week before storing books, and if you use latex paint I suggest you apply a coat of wax after it is thoroughly dried. If you want to make it look better than just boards put together you can buy trim that you can put along the top front edge of the bookcase to make it look better. You can also place the bottom shelf up high enough that you could put a board across the bottom as a "kick" plate. Keep in mind that boards are cut to 1/2 inch of stated size. For example: a board that will be labeled as 1 by 4 will actually be 3-1/2 inches wide and 3/4" thick.

I would suggest you get a drill to make your holes for nails or screws. This would be a wonderful "starter" project that once you have conquered this you will be eager to go on to other projects. (Having said all of the above) you could also make a rough bookcase using bricks and boards. If you go that route, I would suggest gluing some of the bricks together for stabilizaation of the structure. I would look on-line to see if you can find someone who will have a video showing how to make a simple bookcase.

Do you want to make one? If so, here are some ideas. That said, I have a tip or two that will help.

https://www.google.com/search?q=shallow+bookcase+diy&rlz=1C1BLWB_enUS700US700&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi398T056rZAhXGiFQKHXC5DGkQ_AUICygC&biw=1422&bih=629&dpr=1.13#imgrc=_

Some of these are huge and expensive. This is what I would do if you just want to get them up and out of the way.

https://www.google.com/search?q=over+the+door+video+racks&rlz=1C1BLWB_enUS700US700&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi_mNej6KrZAhXGwFQKHciwBHMQ_AUICygC&biw=1422&bih=629&dpr=1.13

And finally, if you want something totally "do it yourself" then I would build your own out of 6" boards and L' brackets. Make sure you hit a stud and if you want them cute and clean, put the bracket on the top of each board so the books hide them.

https://www.google.com/search?q=l+brackets+and+board+bookcases&rlz=1C1BLWB_enUS700US700&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjIxNf76KrZAhUrrFQKHbIkCm4Q_AUICygC&biw=1422&bih=629&dpr=1.13#imgrc=_

You can find more narrow shelves online. We searched for very narrow shelves too, and even through Walmart you can order them very shallow in depth. Montgomery Ward also had some we used.

If you already have a deep bookcase, you can lay 2-4 old paperbacks across the back of each shelf, or use cut off cereal box bottoms or a board about 4” tall. Then you can display books as a back row, and another sitting on the shelf in the front. Two rows, same space, fewer shelves, great for collections with many books by same author, genre, or cover color. Have fun! ☺️