Designing a large format book is a lot trickier than designing mass market paperbacks or the smaller trade cut sizes. The problem with large format books, especially when you get up to the size of a sheet of typewriter paper (8.5" x 11") is that a single text block starts looking like a typewritten page or a handout, rather than a book. There are a number of ways you can minimize this effect, the easiest of which is not to choose a large format unless you have to. Unfortunately, I'm working on a book that includes a number of 6.25" x 9" illustrations, and shrinking them isn't a good option for reasons of legibility.
Perhaps the most common way to cope with large page sizes is to move to a column format, with two columns being the norm. I have seen books designed with three columns, but these are usually pure reference books, or coffee table sizes. One of the pluses of a two column format is it allows for a variety of different illustrations to be used in a natural looking way. Some illustrations may span two columns, others may placed in the outside column, effectively making that column wider for the page. I show a few examples of large format designs in my scruffy looking video, which goes to show what happens when you don't work for anybody:-)
One trick that the major trade publishers have been using for years in designing larger format books for the sake of creating a substantial shelf presence, is to fill the borders with elements. Not useful elements like navigation or calculations, but rather annoying comments like "Note: This is important!" or "Reminder: Have fun while you're working." But now that I find myself stuck producing an 8.25" x 11" book for the sake of fitting my illustrations, I regret my own position on the silly elements issue. Nothing could be easier than filling in some of that white space with harmless little notes, and the book would probably look better for it. But for the time being, I'm going to stick with URLs giving links to color illustrated procedures on my website that I couldn't use in the book.
Most people do like the look of large outside margins, which first time book designers may find counter-intuitive. After all, a large inside margin would make the book easier to read without breaking the spine open. But for whatever the reason, large outside margins are more aesthetically pleasing, perhaps because peripheral vision combines the inside margins of facing pages. In many Victorian and earlier novels, margins were huge in quality printings, and the text block looked more like a newspaper column that had been pasted on a blank page. I was referring to this in the video when I mentioned the "last century" and misspoke 1900's for 1800's. But 2.5" or 3.0" margins carried on for dozens of pages start looking a little strange as well.