A frame for a chalkboard, converted from standard photo frame. I've used 0.6 mm ferrous magnetic vinyl sheet glued to 2.3 mm 240*300 hardboard. 

The whole frame prints in 3 batches and requires 8 to 12 5*2 magnets, depending on your preferred spacing of glass to frame. Leg is fastened using 2 M4x16 DIN 912 screws. 

Magnets can be glued to glass with CA glue.

To use magnet generator script, get fontmeasure library by Apruss from https://cults3d.com/en/3d-model/art/measuring-and-wrapping-text-in-openscad