I saw a few magnetic geometric shape parts to print online and decided I would make some with customised images on them for our 2 year old grandson. The most affordable Neodymium diamagnetic cylindrical magnets available were 12mm long by 3mm diameter. They have a 0.65kg pull which allows parts to be easily snapped together, but they can't be knocked around without collapsing! Increasing the pull force any more starts costing a lot more per magnet.
I have limited shapes to equilateral triangles, squares and pentagons initially. I tried printing each shape in two mirror halves with a rectangular cavity in each side, big enough when mated together to accept a magnet able to spin freely. I used PLA to print and superglue to glue the shape halves with the magnets inserted. It worked fine, but twisting
and bending the shape could break the glue bond enough to let a magnet be pulled outside! I decided to switch to TPU and print with a printer pause at a set layer to insert the magnets, the print completion sealing the magnets inside. This was much stronger, retaining magnets no matter how the shape is twisted. The TPU is much more compliant than PLA and cannot break into sharp peices.