You should set this up as either 8.5 x 11 facing pages, or as 2 11 x 17 non-facing pages (ONLY if the brochure has ony 4 pages). If you are going to use more than one sheet of 11 x 17, set it up as letter-size facing page, do your layout in consecutive page order (reader's spreads) and use Print Booklet to impose if printing in-house, or export to PDF as single pages, not spreads, for commercial printing.

I would do it as two pages. Set the guides appropriately so you can see where the pages are.

Allow for the inside panel to be cut to fit.

Bob

We need to be very clear about waht you mean by a "page" rather than the number of sheets on which this is going to be printed. If the brochure is one sheet of 11 x 17, printed on both sides and folded so it has 4 panels, then you can set it up as a two-page 11 x 17 document. I do it this way most of the time, and set the pages with two columns to make the margins at the gutter where it folds for convenience in layout. Side one (page 1 in the layout) would have the back cover on the left and the front cover onthe right, and side two (page 2 in your layout) would have the two inside "pages."

In theory you can set up a longer document this way, too, but it's so much work to remember the imposition pattern and such a hassle and prone to error to work this way instead of looking at the design as the readers see the finished product, that I would never do it for more pages. Setting up as 8.5 x 11 facing pages is fast, easy to work with, allows for changing the page count if necessary, and works for automatic page numbering, so it just makes more sense to do that if you will be printing more than one sheet of paper.