About 7g of PLA or ABS, a miniature snap-action switch without a lever, a screw to lock the switch into position, and a couple screws to mount it on your printer. Solder wires to the common and NC contacts on the switch, insert a piece of filament through the body, then slide the switch into the slot with the nub in the filament hole. Listen for it to click, then tighten the screw to hold the switch in place. Pull the filament out and make sure the switch closes. Connect the wires to a switch input on your controller board and modify the config file to read the switch and pause the print when it closes.