Here's a simple model to build:

• This model prints on its end, standing upright without the need for support or infill
• The tiles are scalable to any size and so long as they're all printed at the same size, they will all fit together
• The color aesthetic/pattern is limited only by your filament colors
• The back is flat. This surface is for you to use a 3M Command Strip with. You can cut a 3M Command Strip into smaller squares and attach these to your walls without the need for nails or other adhesives. Don't cut them too small though or they won't last and your tiles will fall down.

I would suggest printing with 2 shells at .15mm layer height, and 0% infill (especially if you're using a translucent filament). No supports needed if you've oriented it correctly on the build plate.