Magnetic building board

You can get the magnets for the triangles on Amazon:
https://www.amazon.ca/gp/product/B00IYFO79I/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

And for free building:
https://www.amazon.ca/gp/product/B00IYFO7KM/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Use 1-1/4" #10-32 machine screws to bolt on the magnets to the triangles and use an 18 gauge galvanized steel sheet (mines 24x60") for the building board.

Take a file and make the vertical edge as square to the building surface as you ca