Magnetic building board
thingiverse
You can get the magnets for the triangles on Amazon: https://www.amazon.com/dp/B00IYFO79I/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1 And for free building: https://www.amazon.com/dp/B00IYFO7KM/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1 Use 1-1/4" #10-32 machine screws to bolt the magnets onto the triangles and use an 18 gauge galvanized steel sheet, such as a 24x60" board, for the building surface. Take a file and square up the vertical edge of the building surface as much as possible. It shouldn't need too many adjustments.
With this file you will be able to print Magnetic building board with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Magnetic building board.