An indoor putting green is a finished product rather than a material. It arrives sized, contoured and ready to unroll, usually with breaks already built into the surface so you are reading a putt instead of hitting the same flat stroke over and over.
Pick by two things: the space you have, and whether you want to practice or to score. Training greens are built with defined breaks and target holes to expose a stroke that pushes or pulls. Larger club greens are closer to a real surface and are what you want if the room is the point rather than the drill.
If you would rather cut a green to your own shape, or you are building it into a simulator bay, you want turf by the roll instead.