This is a square shaped box with a magnetic lid. The outer dimensions are 100mmX100mmX60mm. The inner dimensions are 84mmX84mmX50mm.
The magnet holes were designed for round magnets measuring 6mmX1.5mm. The holes were made with slight tolerances and measure 6.2mmX1.6mm.
No supports are needed.
I purchased my magnets from K & J Magnetics, specifically from their surplus section at the time. https://www.kjmagnetics.com
The author hasn't provided the model origin yet.