Warning: In the following description I'm going to use metric units and Danish currency. You'll have to do the math yourself if you want other units but I'll help you out a little:
1 cm = 10 mm. 1 cm = 0.3937 inch
1 kr = 0.134 euro. 1 kr = 0.178 us dollar (give and take, changes a bit every day)
Years back I lived near the second largest library in Denmark and could always get my hands on any book I wanted. A large number of reference works was even always at hand at the reading room. I'm no longer in that fortunate situation so I got interested in doing some book scanning so I could always have these reference works at hand and share them with others who are in the same situation.
Quite a few of these books are very large in format. In some cases the page size is 30 x 40 cm and even though that is not the majority there's still a lot sized 25x35 cm. In other words: To big for the hackerspace scanner. To begin with I thought of making a special version of the hackerspace scanner suited for big books but I realised that might not be the way to go. To name a few reasons:
1. There would be a lot of work involved in upscaling it
2. It would be a huge monster and my appartment isn't that big
3. A scanner built for 30 x 40 cm books wouldn't be ideal for smaller book sizes and after all not all the books I want to scan are huge
So I decided to make a simple solution for the large books and then later on perhaps build a standard hackerspace scanner.
The simplest model would of course be the cardboard box model but it's a bit to "improvised" to my taste. Not a big fan of having to tape down the box to the table either. And perhaps not the best choise for some of the largest books since they are rather heavy. So I took a look at what was at some point called the new standard scanner: http://www.diybookscanner.org/forum/viewtopic.php?f=1&t=333.
And then the concept was born: A cardboard box scanner but without a cardboard box. Instead I would build the cradle from the old new standard scanner (really, version numbers on the standard scanners would be great!). Should I at some point later on feel the need to build a real scanner for the large books I could just use the cradle for that.
Design and materials
Beside scale the only real modification I made to the cradle design was to change the angle from 90 degress to 100 degress. In hindsight I would just have left it at 90 degress. First of all it's simpler, secondly the camera need to be up high to get the right angle on those big books. With the cradle placed on my dinner table (72 cm high) and the camera on a tripod on the floor I almost have the tripod (Hama Star 62) at maximum height (160 cm). And finally it has no significant advantage unless I build an actual scanner around the cradle.
The material are pretty much as described by Daniel. I bought a 16 mm MDF sheet at the size I needed since the shop would cut it for me at the wanted size with no extra charge. I got a 40 x 170 cm sheet, a little more than needed but I figured I better have a little extra. And since the prize was only 81 kr there wasn't much sense in trying to save 5 kr. Same reason I went for 16 mm and not 12 mm. Would have been plenty thick.
And then just some screws, some threaded rod (had to buy 100 cm!), a couple of long bolts and some black paint. Actually I think the paint was the most expensive of those at about 50 kr, at least when you look at how many screws and how much threaded rod I have left whereas I ran out of paint just before having painted the whole thing black. Screws, threaded rod and bolts was something like 100 kr if I remember correctly but I didn't use more than 1/3 of the screws and the threaded rod.
The base plate is 40 x 50 cm and the two angled plates are 30 x 40 cm each. The triangle pieces (4 in total) are something like 19.5 x 13 x 23 cm but please do some math on the size they should be if you copy the design since I just measured mine now and have lost my notes and don't know what size I tried to cut them to be. And then finally there's the piece used to hold the adjustable plate in place where I just used a piece something like 16 x 16 cm big (size not that important).
Beside the cradle I of course needed to get a piece of glass. I use a 32 x 42 cm 2 mm thick non glare piece and so far it works for me. For lights I use a cheap desk lamp from Ikea with an ordinary low energy bulb at 1500 lumens. And finally a tripod for the camera but like the desk lamp I already had that.
Flaws and things to work on
Simply because I haven't done much wood work the last 20 years the finish isn't great. For now I'm just glad it's only a cosmetic problem and not a functional one.
A more serious flaw is that it's hard to get even lighting without glare in this setup. In particular with the really large books where the lamp is close to one part of the side and quite a bit away from the part close to the spine. Only solution I see is to build something so I can have the light directly above the cradle like on a regular scanner but then I'm getting close to what I was not going to build
The angle of the cradle I have already mentioned. Lately I've been thinking about if it actualle needs to be symmetrical for this particular one camera design. As it is now the 100 degress are split equally compared to a vertical line down the middle of the cradle. In principle the side not being photographed could be lying almost flat and the other side standing almost vertical (I use the term "almost" losely") . This should give a less extreme camera positioning but there might be other disadvantages like lighting.
Photos of the scanner
A scanned page
The following photo is of a page from a book with a page size of 39 x 28 cm (same as seen on the photos above). I used a Canon Powershot A810 (16 MP) and the setting were: ISO 200, f/4.5, 1/125 s and a focal length of 12 mm (just over 2x zoom). I've since started using a setting with EV +1 so the photos aren't quite as dark but the book is old and with a bit of a yellow tone. I also should have zoomed in a bit more to get higher DPI (think I landed on 246 DPI here) and aligned things a bit better. Btw, I use the Homer software package ( http://diybookscanner.org/forum/viewtopic.php?f=20&t=2478) to create searchable pdf's after scanning.
First photo is downscaled, second is a piece of the original photo.