My main shelving unit is all from the Billy range at Ikea. I designed it to step up and down with the contour of the ceiling in my attic. It's made up of several different sized shelves:
1 60cm wide full-height unit (my original bookshelf)
2 media shelves designed for DVD's either side
2 40cm wide full-height units either side of that
2 40cm wide half-height units at the ends
2 height extenders that take add another shelf to the half-height units
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The shelves are adjustable except for the middle one in the full height units, which are fixed for the sake of stability. If you have all the shelves of equal height it gives you 30cm's per shelf. This gives you enough space to comfortably fit OHC sized books with finger room at the top. Unfortunately if you need to make room for some bigger volumes (like Fear Agent library editions) you'll need to sacrifice height elsewhere. The shelves adjust in steps of about 3.5 cm, if you take that off one shelf you can still fit TPB's on them comfortably, but nothing else. Strangely enough, the height extenders are slightly taller, they're about 33cm which gives you just enough room for the Fear Agent library editions or similar.
The media units are designed for DVD's and Blu-rays, but you can also fit smaller books on there. I have the shelves about 21cm apart, and generally use them to display comic-related movies and TV shows, trying to store them next to their comic book counterparts. I have all the Timmverse DVD's at the top with my DC collection for example. Each shelf is wide enough for 10 DVD's. If the shelves are spaced similarly to mine there will be some left over shelves, I prop these up at an angle inside the shelves with blue-tac and rest films on them with the covers out, just to make things a bit more interesting.
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In general with my shelves I try to make them look interesting. Rather than shelf labels I face out one book on each shelf that shows what character/type of book is on there. I try to make these OHC's or omni's whee possible. Obviously this can only be done if you have the space, I'm running out on certain shelves, but the space behind the outward-facing book gives room for some hidden overflow.
The 40cm shelves will fit up to 45 normal size TPB's on them, and about 15 OHC's depending on thickness. With an outward facing OHC that cuts the space in half. The shelves are deeper than they need to be for most books, so I pull mine forward to about 1cm from the edge, this just makes them look like they fit better and they seem more pronounced on the shelves that way. It's a good tip for anyone really.
When you make a shelving unit out of multiple shelves they can spread apart a bit at the top, depending on your flooring. The media shelves on mind aren't as deep so they can slip backwards. To neaten things up I just drilled a small hole near the top of each shelf and discretely screwed them to each other to keep them stable. I finished them off with a set of 3 lights on the top which also came from Ikea. Either side I have some floor standing speakers, which I use to complete the downwards slope on each side.
I also have a 4x4 square Expedit shelf from Ikea. I don't really use this for comics at the moment, but I might have to start doing if my collection grows any further. Each shelf gives you slightly more height than my Billy bookcases typically do, with a clearance of just over 33cm. That's a good height for most books, but still not enough for Absolute editions and similar. Unfortunately the heights can't be adjusted, but if you really want to, there is a way to adjust the widths.
If when you're building the unit you decide you need more width, don't fix that shelf in place. Keep it loose, use appropriately sized screws to hold the shelf above and below in place, then just slide the loose shelf into the position you want. It's such a tight fit that it won't go anywhere, I have to use this method to fit my printer on the shelves, which looks like this.
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I hope this has helped someone, for more on my collection I've posted lots of pictures and close-ups on this thread:
http://community.comicbookresources....e-goods!/page7
There's also an article I wrote with some tips about how to organise your shelves if anyone is interested in that sort of thing.
http://wethenerdy.com/five-rules-of-shelf-organisation/