When you make a editorial design, do you make the design layout first or get the content first?

Make a "dummy" first, a thumbnail sketch of the whole brochure idea. Use geometric shapes (squares or rectangles) to represent any image, lines for text instead of words. If it is going to be folded, fold your paper and rough out where your copy and or images will be placed. You can make a dummy in 5 minutes, make several with different layouts, then decide which is more visually apealing or easier for the reader to understand.