You can drag pages near each other in the pages panel. They will click together to make a gatefold IF you first go to the Pages panel menu button flyout and turn off Allow Pages to Shuffle. It might also say Allow selected pages to shuffle. You might turn both switches off. Then, you can drag pages next to each other and they will stick. I usually also turn off Left and Right Facing Pages under File > document setup, too, before I make a gatefold. Lastly, I usually make a gatefold as a separate document from the rest of the pages.
Hope this helps,
Mike Witherell, ACP
I would select the page you want to make the gatefold with the Page Tool in InDesign CC (it's the third tool that is right underneath the Direct Selection Tool (the hollow arrow one) and change the size of the page in the page dimensions fields in the dock at the top of the window.
Assume nothing when doing gatefolds. The first thing you should do is talk to the printer and find out what HE wants.
Thank you Peter. I’ve been leaning in this direction.