People often get hung up on layout. I once worked with someone who insisted on formatting first, setting up text boxes and such, and then filling in the spaces as she wrote. I think this is a mistake. Focus on writing first, then you can flow your content to a template and make adjustments accordingly.
When it does come time to put your case study into layout, it’s always great to have a designer. If you don’t have an in-house person or team, you can hire a contractor to create a simple, inexpensive template for you.
However, a designer isn’t always necessary, especially if you’re short on time or budget. A plain old word processing doc (Word, Google Docs, Open Office, Pages, etc.) will work just fine. If you decide to do the layout yourself, be sure to add your logo and your customer’s logo, and for the love of all that’s good, don’t use a crazy font (Comic Sans, Papyrus, WingDings—I’m looking at you). When you go to print, select print to PDF, or if your system doesn’t offer this functionality, download a simple program that converts word processing files to PDF. Voilà! You now have a completed case study.