I took the saiyanslayer's part as inspiration and designed my own using FreeCAD (source file included, feel free to modify). I use 3x1mm neodym magnets from ebay (10$ incl. shipping for 500 pcs).Make a test print first and adapt scaling of the tolerances are too tight. I use 0.2mm layer height for speed. Let the part cool down long enough so it will not warp. Press in a magnet on each side (with alternating polarity of course, otherwise you'll have a problem). Fix the magnets with a drop of CA glue if they are loose. I used different a different color for the 7 tiles in the center (001 and 1xx).