Here’s a basic Holodeck layout, Enterprise-D version. There are variants in size to an unactivated holodeck, depending on which episode you’re looking at. For the most part, your holodeck adventures will not take place in the room without a program, but there are a few instances in TNG where the bare holodeck was used for exercise classes, or as a place to create devices (such as in “The Nth Degree”).
As a bonus, I’ve also included an Arch that you can print, cut, and assemble into a box shape. For this version, I chose to represent the sides and tops with some perspective, rather than just plain rectangles.
Holodeck Arch (PDF, fold and tape together)
Here are a couple of images that you can copy in case you want to use them as tokens or stand-ups.